U.S. patent application number 13/503975 was filed with the patent office on 2012-09-20 for cation exchange membrane, electrolysis vessel using the same and method for producing cation exchange membrane.
This patent application is currently assigned to ASAHI KASEI CHEMICALS CORPORATION. Invention is credited to Yoshifumi Kado, Hiroyuki Kameyama, Manabu Sugimoto.
Application Number | 20120234674 13/503975 |
Document ID | / |
Family ID | 43921961 |
Filed Date | 2012-09-20 |
United States Patent
Application |
20120234674 |
Kind Code |
A1 |
Kameyama; Hiroyuki ; et
al. |
September 20, 2012 |
CATION EXCHANGE MEMBRANE, ELECTROLYSIS VESSEL USING THE SAME AND
METHOD FOR PRODUCING CATION EXCHANGE MEMBRANE
Abstract
A cation exchange membrane includes: a membrane body containing
a fluorine-based polymer having an ion-exchange group; and two or
more reinforcing core materials arranged approximately in parallel
within the membrane body. The membrane body is provided with two or
more elution holes formed between the reinforcing core materials
adjacent to each other. A distance between the reinforcing core
materials adjacent to each other is represented by a, a distance
between the reinforcing core materials and the elution holes
adjacent to each other is represented by b, a distance between the
elution holes adjacent to each other is represented by c, and the
number of the elution holes formed between the reinforcing core
materials adjacent to each other is represented by n. The
relationship represented by the following expression (1) or
expression (2) are satisfied: b>a/(n+1) (1); c>a/(n+1)
(2)
Inventors: |
Kameyama; Hiroyuki;
(Chiyoda-ku, JP) ; Sugimoto; Manabu; (Chiyoda-ku,
JP) ; Kado; Yoshifumi; (Chiyoda-ku, JP) |
Assignee: |
ASAHI KASEI CHEMICALS
CORPORATION
Tokyo
JP
|
Family ID: |
43921961 |
Appl. No.: |
13/503975 |
Filed: |
October 25, 2010 |
PCT Filed: |
October 25, 2010 |
PCT NO: |
PCT/JP2010/068855 |
371 Date: |
May 29, 2012 |
Current U.S.
Class: |
204/252 ;
204/295; 28/168 |
Current CPC
Class: |
C09K 13/00 20130101;
H01M 8/1053 20130101; H01M 8/1062 20130101; C25B 13/02 20130101;
C25B 13/08 20130101; H01M 8/106 20130101; C08J 5/2206 20130101;
Y02E 60/50 20130101; C08J 2327/12 20130101; H01M 8/1076 20130101;
H01M 8/1079 20130101; H01M 2300/0082 20130101; H01M 8/1039
20130101; H01M 8/1023 20130101; H01M 8/1067 20130101; Y02P 70/50
20151101 |
Class at
Publication: |
204/252 ;
204/295; 28/168 |
International
Class: |
C25B 13/04 20060101
C25B013/04; D06Q 1/02 20060101 D06Q001/02; C25B 9/08 20060101
C25B009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 26, 2009 |
JP |
2009-245869 |
Claims
1. A cation exchange membrane at least comprising: a membrane body
containing a fluorine-based polymer having an ion-exchange group;
and two or more reinforcing core materials arranged approximately
in parallel within the membrane body, wherein the membrane body is
provided with two or more elution holes formed between the
reinforcing core materials adjacent to each other, and assuming
that a distance between the reinforcing core materials adjacent to
each other is represented by a, a distance between the reinforcing
core materials and the elution holes adjacent to each other is
represented by b, a distance between the elution holes adjacent to
each other is represented by c, and the number of the elution holes
formed between the reinforcing core materials adjacent to each
other is represented by n, then a, b, c, and n satisfying the
relationship represented by the following expression (1) or
expression (2) are at least present. b>a/(n+1) (1) c>a/(n+1)
(2)
2. The cation exchange membrane according to claim 1, wherein a, c,
and n further satisfy the relationship represented by the following
expression (3). 0.2a/(n+1).ltoreq.c.ltoreq.0.9a/(n+1) (3)
3. The cation exchange membrane according to claim 1, wherein a, b,
and n further satisfy the relationship represented by the following
expression (4). a/(n+1)<b.ltoreq.1.8a/(n+1) (4)
4. The cation exchange membrane according to claim 1, wherein a, c,
and n further satisfy the relationship represented by the following
expression (5). 1.1a/(n+1).ltoreq.c.ltoreq.0.8a (5)
5. The cation exchange membrane according to claim 1, wherein a
first interval between the reinforcing core materials in which a,
b, c, and n satisfy the relationship represented by the expression
(1), and a second interval between the reinforcing core materials
in which a, b, c, and n satisfy the relationship represented by the
expression (2) are alternately present.
6. The cation exchange membrane according to claim 5, wherein in
the first interval between the reinforcing core materials, a, b, c,
and n further satisfy the relationships represented by the
following expression (3) and the following expression (4), and in
the second interval between the reinforcing core materials, a, b,
c, and n further satisfy the relationship represented by the
following expression (5). 0.2a/(n+1).ltoreq.c.ltoreq.0.9a/(n+1) (3)
a/(n+1)<b.ltoreq.1.8a/(n+1) (4) 1.1a/(n+1).ltoreq.c.ltoreq.0.8a
(5)
7. The cation exchange membrane according to claim 5, wherein the
first interval between the reinforcing core materials satisfying
the relationship represented by the following expression (6) and
the second interval between the reinforcing core materials
satisfying the relationship represented by the following expression
(7) are alternately present. n=2,b>a/3 (6) n=2,c>a/3 (7)
8. The cation exchange membrane according to claim 5, wherein the
first interval between the reinforcing core materials satisfying
the relationship represented by the following expression (8) and
the second interval between the reinforcing core materials
satisfying the relationship represented by the following expression
(9) are alternately present.
n=2,0.2a/3.ltoreq.c.ltoreq.0.9a/3,a/3<b.ltoreq.1.8a/3 (8)
n=2,1.1a/3.ltoreq.c.ltoreq.0.8 (9)
9. The cation exchange membrane according to claim 1, wherein a, b,
c, and n satisfying the relationship represented by the above
expression (1) or the above expression (2) are at least present in
a MD direction and in a TD direction of the cation exchange
membrane.
10. The cation exchange membrane according to claim 6, wherein the
first interval between the reinforcing core materials satisfying
the relationships represented by the expression (3) and the
expression (4) or the second interval between the reinforcing core
materials satisfying the relationship represented by the expression
(5) is present in the MD direction and in the TD direction of the
cation exchange membrane.
11. A method for producing the cation exchange membrane, comprising
the steps of: weaving two or more reinforcing core materials, a
sacrifice yarn soluble in an acid or an alkali, and a dummy yarn
soluble in a predetermined solvent in which the reinforcing core
materials and the sacrifice yarn are insoluble, to obtain a
reinforcing material having the sacrifice yarn and the dummy yarn
arranged between the reinforcing core materials adjacent to each
other; soaking the reinforcing material in the predetermined
solvent to remove the dummy yarn from the reinforcing material;
stacking the reinforcing material from which the dummy yarn is
removed and a fluorine-based polymer having an ion-exchange group
or an ion-exchange group precursor which can be converted into the
ion-exchange group by hydrolysis, to form a membrane body having
the reinforcing material; and soaking the sacrifice yarn in an acid
or an alkali to remove the sacrifice yarn from the membrane body,
thereby forming an elution hole in the membrane body.
12. An electrolysis vessel at least comprising: an anode; a
cathode; and the cation exchange membrane according to claim 1
arranged between the anode and the cathode.
13. The cation exchange membrane according to claim 2, wherein a,
b, and n further satisfy the relationship represented by the
following expression (4). a/(n+1)<b.ltoreq.1.8a/(n+1) (4)
14. The cation exchange membrane according to claim 2, wherein a
first interval between the reinforcing core materials in which a,
b, c, and n satisfy the relationship represented by the expression
(1), and a second interval between the reinforcing core materials
in which a, b, c, and n satisfy the relationship represented by the
expression (2) are alternately present.
15. The cation exchange membrane according to claim 14, wherein in
the first interval between the reinforcing core materials, a, b, c,
and n further satisfy the relationships represented by the
following expression (3) and the following expression (4), and in
the second interval between the reinforcing core materials, a, b,
c, and n further satisfy the relationship represented by the
following expression (5). 0.2a/(n+1).ltoreq.c.ltoreq.0.9a/(n+1) (3)
a/(n+1)<b.ltoreq.1.8a/(n+1) (4) 1.1a/(n+1).ltoreq.c.ltoreq.0.8a
(5)
16. The cation exchange membrane according to claim 14, wherein the
first interval between the reinforcing core materials satisfying
the relationship represented by the following expression (6) and
the second interval between the reinforcing core materials
satisfying the relationship represented by the following expression
(7) are alternately present. n=2,b>a/3 (6) n=2,c>a/3 (7)
17. The cation exchange membrane according to claim 14, wherein the
first interval between the reinforcing core materials satisfying
the relationship represented by the following expression (8) and
the second interval between the reinforcing core materials
satisfying the relationship represented by the following expression
(9) are alternately present.
n=2,0.2a/3.ltoreq.c.ltoreq.0.9a/3,a/3<b.ltoreq.1.8a/3 (8)
n=2,1.1a/3.ltoreq.c.ltoreq.0.8 (9)
18. The cation exchange membrane according to claim 15, wherein the
first interval between the reinforcing core materials satisfying
the relationships represented by the expression (3) and the
expression (4) or the second interval between the reinforcing core
materials satisfying the relationship represented by the expression
(5) is present in the MD direction and in the TD direction of the
cation exchange membrane.
19. An electrolysis vessel at least comprising: an anode; a
cathode; and the cation exchange membrane according to claim 2
arranged between the anode and the cathode.
Description
TECHNICAL FIELD
[0001] The present invention relates to a cation exchange membrane,
an electrolysis vessel using the same and a method for producing
the cation exchange membrane.
BACKGROUND ART
[0002] A fluorine-containing ion exchange membrane is excellent in
e.g., heat resistance and chemical resistance. Therefore, the
fluorine-containing ion exchange membrane has been used not only as
a cation exchange membrane for alkali chloride electrolysis for
producing chlorine and an alkali but also a diaphragm for
generating ozone, a fuel cell, wide variety of diaphragms for
electrolysis such as water electrolysis and hydrochloric acid
electrolysis. Of them, the membrane for use in alkali chloride
electrolysis is demanded to, e.g., increase current efficiency in
view of productivity, reduce electrolysis voltage in view of
economic efficiency and reduce the concentration of sodium chloride
in caustic soda in view of quality of a product.
[0003] Of these demands, in order to increase current efficiency,
an ion exchange membrane formed of at least two layers, i.e., a
carboxylic acid layer using a carboxylic acid group having high
anion elimination property as an ion-exchange group and a sulfonic
acid layer using a low resistant sulfonic acid group as an
ion-exchange group, is generally used. Since these ion exchange
membranes are brought into direct contact with chlorine and caustic
soda of from 80 to 90.degree. C. during an electrolysis operation,
a fluorine-based polymer having extremely high chemical resistance
is used as a material for the ion exchange membrane. However, the
ion exchange membrane formed of such a fluorine-based polymer alone
does not have sufficient mechanical strength. Therefore, the
membrane is reinforced, for example, by embedding a woven fabric
contained of polytetrafluoroethylene (PTFE) in the membrane, as a
reinforcing core material.
[0004] For example, Patent Document 1 proposes a fluorine-based
cation exchange membrane for electrolysis composed of a first
layer, which is formed of a fluorine-based polymer film having a
cation-exchange group and reinforced with the woven fabric, and a
second layer, which is formed of a fluorine based polymer having a
carboxylic acid group and positioned on the cathode side, in which
.gtoreq.1/2 of the thickness of a porous base material is projected
from the first layer toward the anode side, the projecting part of
the porous base material is covered with a coating layer of the
fluorine-based polymer having the cation-exchange group so as to
integrate into the first layer and to form the convexo-concaves
along with the surface shape of the porous base material on the
anode side surface. [0005] Patent Document 1: Japanese Patent
Application Laid-Open No. 4-308096
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0006] However, the reinforcing core material acts as a blocking
material for a cation such as alkali ion when flowing from the
anode side to the cathode side within the membrane thereby
preventing the cation from flowing from the anode side to the
cathode side smoothly. To solve this phenomenon, a hole
(hereinafter, referred to as an "elution hole") is formed in the
cation exchange membrane for ensuring a flow channel for e.g., a
cation and an electrolyte and used as an electrolyte flow channel.
In this manner, the electrical resistance of the cation exchange
membrane is expected to be reduced. However, the strength of the
cation exchange membrane is reduced by the presence of the elution
hole. Particularly, in the case where the cation exchange membrane
is mounted to an electrolysis vessel and the case where the cation
exchange membrane is carried, the cation exchange membrane folds or
bends thereby generating a problem of likely developing a pinhole
from the elution hole. In the cation exchange membrane disclosed in
Patent Document 1, the reinforcing core material projects from the
cation exchange membrane. Therefore, when the cation exchange
membrane rubs against an electrode or the like due to e.g.,
vibration within an electrolysis vessel, a resin covering the
reinforcing core material is peeled off and the reinforcing core
material is exposed therefrom, causing a problem of losing the
function as a reinforcing member.
[0007] In addition, when the cation exchange membrane is mounted to
the electrolysis vessel to perform electrolysis, reduction in
voltage (electrolysis voltage) required for electrolysis is
demanded. To realize this, the cation exchange membrane has
desirably low resistance. Furthermore, the cation exchange membrane
capable of delivering stable electrolytic performance for a long
time is desired.
[0008] The present invention has been made in view of the
aforementioned circumstances. It is a main object of the present
invention is to provide a cation exchange membrane having excellent
mechanical strength against folding or the like, delivering stable
electrolytic performance for a long time, an electrolysis vessel
using the cation exchange membrane and a method for producing the
cation exchange membrane.
Means for Solving the Problems
[0009] The present inventors have made intensive studies with the
view for attaining the aforementioned objects. As a result, they
found that aforementioned objects can be attained by a cation
exchange membrane having at least a membrane body containing a
fluorine-based polymer having an ion-exchange group and two or more
reinforcing core materials arranged approximately in parallel
within the membrane body, in which the membrane body has two or
more elution holes formed between the reinforcing core materials
adjacent to each other, and assuming that a distance between the
reinforcing core materials adjacent to each other is represented by
a; a distance between the reinforcing core materials and the
elution holes adjacent to each other is represented by b; a
distance between the elution holes adjacent to each other is
represented by c; and the number of the elution holes formed
between the reinforcing core materials adjacent to each other is
represented by n, then a, b, c, and n satisfying a specific
relational expression are present. Based on this, the present
invention has been accomplished.
[0010] More specifically, the present invention is as follows.
[1] A cation exchange membrane at least comprising:
[0011] a membrane body containing a fluorine-based polymer having
an ion-exchange group; and
[0012] two or more reinforcing core materials arranged
approximately in parallel within the membrane body,
[0013] wherein the membrane body is provided with two or more
elution holes formed between the reinforcing core materials
adjacent to each other, and
[0014] assuming that a distance between the reinforcing core
materials adjacent to each other is represented by a, a distance
between the reinforcing core materials and the elution holes
adjacent to each other is represented by b, a distance between the
elution holes adjacent to each other is represented by c, and the
number of the elution holes formed between the reinforcing core
materials adjacent to each other is represented by n, then a, b, c,
and n satisfying the relationship represented by the following
expression (1) or expression (2) are at least present.
b>a/(n+1) (1)
c>a/(n+1) (2)
[2] The cation exchange membrane according to [1], wherein a, c,
and n further satisfy the relationship represented by the following
expression (3).
0.2a/(n+1).ltoreq.c.ltoreq.0.9a/(n+1) (3)
[3] The cation exchange membrane according to [1] or [2], wherein
a, b, and n further satisfy the relationship represented by the
following expression (4).
a/(n+1)<b.ltoreq.1.8a/(n+1) (4)
[4] The cation exchange membrane according to [1] or [3], wherein
a, c, and n further satisfy the relationship represented by the
following expression (5).
1.1a/(n+1).ltoreq.c.ltoreq.0.8a (5)
[5] The cation exchange membrane according to any one of [1] to
[4], wherein
[0015] a first interval between the reinforcing core materials in
which a, b, c, and n satisfy the relationship represented by the
expression (1), and
[0016] a second interval between the reinforcing core materials in
which a, b, c, and n satisfy the relationship represented by the
expression (2) are alternately present.
[6] The cation exchange membrane according to [5], wherein
[0017] in the first interval between the reinforcing core
materials, a, b, c, and n further satisfy the relationships
represented by the following expression (3) and the following
expression (4), and
[0018] in the second interval between the reinforcing core
materials, a, b, c, and n further satisfy the relationship
represented by the following expression (5).
0.2a/(n+1).ltoreq.c.ltoreq.0.9a/(n+1) (3)
a/(n+1)<b.ltoreq.1.8a/(n+1) (4)
1.1a/(n+1).ltoreq.c.ltoreq.0.8a (5)
[7] The cation exchange membrane according to [5] or [6], wherein
the first interval between the reinforcing core materials
satisfying the relationship represented by the following expression
(6) and the second interval between the reinforcing core materials
satisfying the relationship represented by the following expression
(7) are alternately present.
n=2,b>a/3 (6)
n=2,c>a/3 (7)
[8] The cation exchange membrane according to any one of [5] to
[7], wherein the first interval between the reinforcing core
materials satisfying the relationship represented by the following
expression (8) and the second interval between the reinforcing core
materials satisfying the relationship represented by the following
expression (9) are alternately present.
n=2,0.2a/3.ltoreq.c.ltoreq.0.9a/3,a/3<b.ltoreq.1.8a/3 (8)
n=2,1.1a/3.ltoreq.c.ltoreq.0.8 (9)
[9] The cation exchange membrane according to [1], wherein a, b, c,
and n satisfying the relationship represented by the above
expression (1) or the above expression (2) are at least present in
a MD direction and in a TD direction of the cation exchange
membrane. [10] The cation exchange membrane according to [6],
wherein the first interval between the reinforcing core materials
satisfying the relationships represented by the expression (3) and
the expression (4) or the second interval between the reinforcing
core materials satisfying the relationship represented by the
expression (5) is present in the MD direction and in the TD
direction of the cation exchange membrane. [11] A method for
producing the cation exchange membrane, comprising the steps
of:
[0019] weaving two or more reinforcing core materials, a sacrifice
yarn soluble in an acid or an alkali, and a dummy yarn soluble in a
predetermined solvent in which the reinforcing core materials and
the sacrifice yarn are insoluble, to obtain a reinforcing material
having the sacrifice yarn and the dummy yarn arranged between the
reinforcing core materials adjacent to each other;
[0020] soaking the reinforcing material in the predetermined
solvent to remove the dummy yarn from the reinforcing material;
[0021] stacking the reinforcing material from which the dummy yarn
is removed and a fluorine-based polymer having an ion-exchange
group or an ion-exchange group precursor which can be converted
into the ion-exchange group by hydrolysis, to form a membrane body
having the reinforcing material; and
[0022] soaking the sacrifice yarn in an acid or an alkali to remove
the sacrifice yarn from the membrane body, thereby forming an
elution hole in the membrane body.
[12] An electrolysis vessel at least comprising: an anode; a
cathode; and the cation exchange membrane according to any one of
[1] to [10] arranged between the anode and the cathode.
Advantageous Effects of the Invention
[0023] According to the present invention, it is possible to
provide the cation exchange membrane having excellent mechanical
strength against folding, etc. and capable of delivering stable
electrolytic performance for a long time, and the method for
producing the cation exchange membrane.
BRIEF DESCRIPTION OF DRAWINGS
[0024] FIG. 1 shows a sectional side view of the first embodiment
of the cation exchange membrane according to the present
embodiment.
[0025] FIG. 2 shows a conceptual diagram of the first embodiment of
the cation exchange membrane according to the present
embodiment.
[0026] FIG. 3 shows a conceptual diagram of the second embodiment
of the cation exchange membrane according to the present
embodiment.
[0027] FIG. 4 shows a conceptual diagram of the third embodiment of
the cation exchange membrane according to the present
embodiment.
[0028] FIG. 5 shows a conceptual diagram of the fourth embodiment
of the cation exchange membrane according to the present
embodiment.
[0029] FIG. 6 shows a conceptual diagram of the fifth embodiment of
the cation exchange membrane according to the present
embodiment.
[0030] FIG. 7 shows a conceptual diagram for illustrating an
example of the producing method according to the present
embodiment.
[0031] FIG. 8 shows a conceptual diagram of a cation exchange
membrane prepared in Examples and Comparative Examples.
[0032] FIG. 9 shows a conceptual diagram of another cation exchange
membrane prepared in Examples and Comparative Examples.
[0033] FIG. 10 shows a conceptual diagram of the electrolysis
vessel according to the present embodiment.
MODES FOR CARRYING OUT THE INVENTION
[0034] Hereinafter, the best mode for carrying out the present
invention (hereinafter referred to as "the present embodiment")
will be more specifically described. Note that, the present
invention is not limited to the present embodiments below and can
be modified in various ways within the scope thereof and carried
out. Note that, in the drawings, the positional relationship such
as right-left or up-down, is based on the positional relationship
shown in the drawings unless otherwise specified. Furthermore, the
dimensional ratio of a drawing is not limited to that shown in the
drawing.
<Cation Exchange Membrane>
[0035] FIG. 1 is a sectional side view of a first embodiment of the
cation exchange membrane according to the present embodiment. FIG.
2 is a conceptual diagram of a first embodiment of the cation
exchange membrane according to the present embodiment. A cation
exchange membrane 1 is a cation exchange membrane at least
comprising: a membrane body 14 containing a fluorine-based polymer
having an ion-exchange group; and two or more reinforcing core
materials 10 arranged approximately in parallel within the membrane
body 14. The membrane body 14 is provided with two or more elution
holes 12 formed between the reinforcing core materials 10 adjacent
to each other. In addition, assuming that a distance between the
reinforcing core materials 10 adjacent to each other is represented
by a, a distance between the reinforcing core materials 10 and the
elution holes 12 adjacent to each other is represented by b, a
distance between the elution holes 12 adjacent to each other is
represented by c, and the number of the elution holes 12 formed
between the reinforcing core materials 10 adjacent to each other is
represented by n, then a, b, c, and n satisfying the relationship
represented by the following expression (1) or expression (2) are
at least present.
b>a/(n+1) (1)
c>a/(n+1) (2)
[0036] The membrane body 14 has a function of selectively passing a
cation and contains a fluorine-based polymer. The membrane body 14
preferably has at least a sulfonic acid layer 142 having a sulfonic
acid group as the ion-exchange group and a carboxylic acid layer
144 having a carboxylic acid group as the ion-exchange group.
Generally, the cation exchange membrane 1 is used such that the
sulfonic acid layer 142 is positioned on the anode side (.alpha.)
of the electrolysis vessel and the carboxylic acid layer 144 is
positioned on the cathode side (.beta.) of the electrolysis vessel.
The sulfonic acid layer 142 is formed of a low
electrical-resistance material and preferably has a large film
thickness in view of membrane strength. The carboxylic acid layer
144 preferably has a high anion elimination property even if the
film thickness is low. By containing the carboxylic acid layer 144
as mentioned above, selective permeability of a cation such as a
sodium ion can be further improved. The membrane body 14 is
satisfactory as long as it has a function of selectively passing
the cation and contains a fluorine-based polymer, and the structure
thereof is not necessarily limited to the aforementioned structure.
The term "anion elimination property" used herein refers to a
property of preventing invasion or permeation of an anion into the
cation exchange membrane.
[0037] The fluorine-based polymer used in the membrane body 14 may
include a fluorine-based polymer having an ion-exchange group or an
ion-exchange group precursor which can be converted into an
ion-exchange group by hydrolysis, formed of a fluorinated
hydrocarbon as a main chain with a functional group capable of
converting into an ion-exchange group by e.g., hydrolysis as a
pendant side chain and to which melt processing is applicable. An
example of the method for producing such the fluorine-based polymer
will be described below.
[0038] The fluorine-based polymer can be produced by, for example,
copolymerization of at least one monomer selected from the
following first group and at least one monomer selected from the
following second group and/or the following third group, or
alternatively produced by homo-polymerization of one monomer
selected from any one of the following first group, second group
and third group.
[0039] The first group monomer may include, for example, a vinyl
fluoride compound. Examples of the vinyl fluoride compound may
include vinyl fluoride, tetrafluoroethylene, hexafluoropropylene,
vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene and
perfluoro(alkylvinylether). Particularly, in the case where the
cation exchange membrane 1 according to the present embodiment is
used as a membrane for alkali electrolysis, a perfluoro monomer is
preferably used as the vinyl fluoride compound. For example, a
perfluoro monomer selected from the group consisting of
tetrafluoroethylene, hexafluoropropylene and
perfluoro(alkylvinylether) is preferable.
[0040] The second group monomer may include, for example, a vinyl
compound having a functional group capable of converting into a
carboxylic acid group (carboxylic acid type ion-exchange group).
The vinyl compound having a functional group capable of converting
into a carboxylic acid group (carboxylic acid type ion-exchange
group) may include, for example, a monomer represented by
CF.sub.2.dbd.CF(OCF.sub.2CYF).sub.s--O(CZF).sub.t--COOR (wherein s
represents an integer of 0 to 2, t represents an integer of 1 to
12, Y and Z each independently represent F or CF.sub.3 and R
represents a lower alkyl group) and the like.
[0041] Of these, a compound represented by
CF.sub.2.dbd.CF(OCF.sub.2CYF).sub.n--O(CF.sub.2).sub.m--COOR is
preferable, where n represents an integer of 0 to 2, m represents
an integer of 1 to 4, Y represents F or CF.sub.3 and R represents
CH.sub.3, C.sub.2H.sub.5 or C.sub.3H.sub.7. Particularly, when the
cation exchange membrane according to the present embodiment is
used as a cation exchange membrane for alkali electrolysis, at
least a perfluoro compound is preferably used as a monomer.
However, since the alkyl group (see the aforementioned R) of the
ester group is removed from the polymer at the time of hydrolysis,
the alkyl group (R) may not be a perfluoroalkyl group where all
hydrogen atoms are substituted with fluorine atoms. Of these, for
example, the monomers shown below are more preferable;
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2COOCH.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)O(CF.sub.2).sub.2COOCH.sub.3,
CF.sub.2.dbd.CF[OCF.sub.2CF(CF.sub.3)].sub.2O(CF.sub.2).sub.2COOCH.sub.3-
,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)O(CF.sub.3).sub.3COOCH.sub.3,
CF.sub.2.dbd.CFO(CF.sub.2).sub.2COOCH.sub.3,
CF.sub.2.dbd.CFO(CF.sub.2).sub.3COOCH.sub.3.
[0042] The third group monomer may include, for example, a vinyl
compound having a functional group capable of converting into a
sulfonic acid group (sulfone type ion-exchange group). As the vinyl
compound having a functional group capable of converting into a
sulfonic acid group (sulfone type ion-exchange group), for example,
a monomer represented by CF.sub.2.dbd.CFO--X--CF.sub.2--SO.sub.2F
is preferable (wherein X represents a perfluoro group). Specific
examples thereof may include the monomers shown below:
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2SO.sub.2F,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2CF.sub.2SO.sub.2F,
CF.sub.2.dbd.CF(CF.sub.2).sub.2SO.sub.2F,
CF.sub.2.dbd.CFO[CF.sub.2CF(CF.sub.3)O].sub.2CF.sub.2CF.sub.2SO.sub.2F,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.2OCF.sub.3)OCF.sub.2CF.sub.2SO.sub.2F.
[0043] Of these,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2CF.sub.2SO.sub.2F,
and CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2SO.sub.2F
are more preferable.
[0044] From these monomers, copolymers can be produced by a
polymerization method developed for homo-polymerization and
copolymerization of ethylene fluoride, particularly, a general
polymerization method used for tetrafluoroethylene. For example, in
a non-aqueous method, a polymerization reaction can be carried out
using an inert solvent such as perfluorohydrocarbon and
chlorofluorocarbon in the presence of a radical polymerization
initiator such as a perfluorocarbon peroxide and an azo compound
under the conditions: a temperature of 0 to 200.degree. C. and a
pressure of 0.1 to 20 MPa.
[0045] In the above-mentioned copolymerization, the kind of
combination of the above-mentioned monomers and the ratio thereof
are not particularly limited, and selected and determined depending
upon the type and amount of functional group that is desired to be
added to the fluorine-based polymer to be obtained. For example, in
order to obtain a fluorine-based polymer containing only a
carboxylate functional group, at least one kind of monomer may be
selected each from the aforementioned first group and second group
and copolymerized. Furthermore, in order to obtain a polymer
containing only a sulfonyl fluoride functional group, at least one
kind of monomer may be selected each from the aforementioned first
group and third group and copolymerized. Moreover, in order to
obtain a fluorine-based polymer having a carboxylate functional
group and a sulfonyl fluoride functional group, at least one kind
of monomer may be selected each from the aforementioned first
group, second group and third group and copolymerized. In this
case, a desired fluorine-based polymer may be obtainable also by
separately polymerizing a copolymer formed of monomers selected
from the aforementioned first group and second group and a
copolymer formed of monomers selected from the aforementioned first
group and third group and thereafter mixing them. Furthermore, the
mixing ratio of the monomers is not particularly limited; however,
in order to increase the amount of functional group per unit
polymer, the ratio of monomers selected from the aforementioned
second group and third group may be increased.
[0046] The total ion exchange capacity of a fluorine containing
copolymer is not particularly limited; however, it is preferably
from 0.5 to 2.0 mg equivalent/g in terms of a dry resin and more
preferably from 0.6 to 1.5 mg equivalent/g in terms of a dry resin.
The total ion exchange capacity used herein refers to an equivalent
of an exchange group per unit weight of a dry resin and can be
determined by neutralization titration, etc.
[0047] The cation exchange membrane 1 of the present embodiment
preferably further has coating layers 146, 148, if necessary, in
view of preventing deposition of gas on the cathode-side surface
and the anode-side surface. The material for constituting the
coating layers 146, 148 is not particularly limited; however, in
view of preventing deposition of a gas, an inorganic substance is
preferably included. Examples of the inorganic substance may
include zirconium oxide and titanium oxide. A method for forming
the coating layers 146, 148, is not particularly limited and a
method known in the art can be used. For example, a method of
coating a liquid having inorganic oxide fine particles dispersed in
a binder polymer solution by a spray, etc., can be mentioned.
[0048] The cation exchange membrane 1 has two or more reinforcing
core materials 10 arranged approximately in parallel within the
membrane body 14. The reinforcing core material 10 refers to a
member for improving mechanical strength of the cation exchange
membrane 1 and dimensional stability thereof. The dimensional
stability as used herein refers to a property of suppressing the
expansion and contraction of the cation exchange membrane within a
desired range. The cation exchange membrane having excellent
dimensional stability does not expand and contract more than
necessary by e.g., hydrolysis and electrolysis and has stable
dimensions for a long time. The member for constituting the
reinforcing core material 10 may be, but not particularly limited
to, for example, a reinforcing core material formed from a
reinforcing yarn. The reinforcing yarn used herein is a member for
constituting the reinforcing core material and refers to a yarn
capable of imparting desired mechanical strength to the cation
exchange membrane and being stably present in the cation exchange
membrane.
[0049] The form of the reinforcing core material 10 is not
particularly limited; however, for example, a woven fabric, a
nonwoven fabric and a knitted fabric using the aforementioned
reinforcing yarn may be used. Of these, in view of convenience in
production, a woven fabric is preferable. As a weave of the woven
fabric, a plain weave is preferable. The thickness of the woven
fabric is not particularly limited; however, it is preferably from
30 to 250 .mu.m and more preferably from 30 to 150 .mu.m.
Furthermore, the weave density (the number of woven fibers per unit
length) of the reinforcing yarn is not particularly limited;
however, it is preferably from 5 to 50 yarns/inch.
[0050] The opening ratio of the reinforcing core material 10 is not
particularly limited; however, it is preferably 30% or more and 90%
or less. The opening ratio is preferably 30% or more in view of the
electrochemical properties of the cation exchange membrane and
preferably 90% or less in view of the mechanical strength of the
membrane. More preferably, the opening ratio is 50% or more and
further preferably 60% or more.
[0051] The opening ratio herein refers to a ratio of the (B) sum of
areas through which a substance such as an ion can pass relative to
the (A) sum of the surface areas of the cation exchange membrane
and represented by (B)/(A). The (B) represents the sum of areas
through which a cation and an electrolyte, etc. can pass without
being interrupted by e.g., the reinforcing core material and the
reinforcing yarn, etc. contained in the cation exchange membrane. A
method for determining the opening ratio will be more specifically
described. A surface image of the cation exchange membrane (cation
exchange membrane before coating) is shot. The areas of the regions
where no reinforcing core material is present are sum up to obtain
the (B). Subsequently, from the area of the surface image of the
cation exchange membrane, the (A) is obtained. The (B) is divided
by the (A) to obtain the opening ratio.
[0052] The material for the reinforcing yarn constituting the
reinforcing core material 10 is not particularly limited; however,
it is preferably a material having resistance to an acid and an
alkali, etc. Particularly, a material containing a fluorine-based
polymer is more preferable in view of maintaining heat resistance
and chemical resistance for a long time. Examples of the
fluorine-based polymer referred to herein, may include a
polytetrafluoroethylene (PTFE), a
tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), a
ethylene-tetrafluoroethylene copolymer (ETFE), a
tetrafluoroethylene-hexafluoropropylene copolymer, a
trifluorochlorethylene-ethylene copolymer and a polyvinylidene
fluoride (PVDF). Of these, polytetrafluoroethylene (PTFE) is
preferable in view of heat resistance and chemical resistance.
[0053] The diameter of the reinforcing yarn to be used in the
reinforcing core material 10 is not particularly limited; however,
it is preferably from 20 to 300 deniers and more preferably from 50
to 250 deniers. The reinforcing yarn may be a monofilament or a
multi-filament. Furthermore, a yarn thereof, a slit yarn, etc. can
be used.
[0054] Particularly preferable form of the reinforcing core
material 10 is a reinforcing core material containing PTFE in view
of chemical resistance and heat resistance, and a tape yarn or a
highly oriented monofilament in view of strength. Specifically, a
tape yarn prepared by slicing a highly strong porous sheet formed
of PTFE into tape-form pieces or a plain-weave using a highly
oriented monofilament formed of PTFE of from 50 to 300 deniers with
a weave density of from 10 to 50 yarns/inch is preferable and the
reinforcing core material having a thickness within the range of
from 50 to 100 .mu.m is more preferable. Furthermore, the opening
ratio of the cation exchange membrane containing the reinforcing
core material is further preferably 60% or more.
[0055] In the membrane body 14, two or more elution holes 12 are
formed. The elution holes 12 are holes that can be used as a flow
channel of a cation generated in electrolysis and an electrolyte.
By forming the elution holes 12, mobility of an alkali ion
generated in electrolysis and an electrolyte can be ensured. The
shape of the elution holes 12 is not particularly limited. In the
case where the cation exchange membrane is produced in accordance
with the process described later, the elution holes 12 of the
membrane body are formed by dissolving a sacrifice yarn in an acid
or an alkali, thus the shape of the elution holes 12 is same as the
shape of the sacrifice yarn.
[0056] As shown in FIG. 1, the cation exchange membrane 1 has
elution holes 12a formed in the perpendicular direction to the
plane of paper and an elution hole 12b formed along the
longitudinal direction in parallel to the plane of paper. That is,
the elution hole 12b formed along the longitudinal direction in
parallel to the plane of paper is formed approximately in
perpendicular to the reinforcing core material 10. The elution hole
12b is preferably formed such that the elution hole 12b alternately
passes through the anode side (side near the sulfonic acid layer
142) and the cathode side (side near the carboxylic acid layer 144)
of the reinforcing core material 10. Owing to such a structure, in
the portion where the elution hole 12b is formed on the cathode
side of the reinforcing core material 10, a cation (for example,
sodium ion) transported through the electrolyte charged in the
elution hole can flow also on the cathode side of the reinforcing
core material 10. As a result, since a cation flow is not
interrupted, the electrical resistance of the cation exchange
membrane 1 can be further reduced.
[0057] Note that, in FIG. 1, the cation exchange membrane 1 has
elution holes 12a formed in the perpendicular direction to the
plane of paper and the elution hole 12b formed along the
longitudinal direction in parallel to the plane of paper. The
number n of the elution holes 12 formed between the reinforcing
core materials 10 adjacent to each other refers to the number of
elution holes 12 arranged in the same direction. In the case of
FIG. 1, the number of elution holes 12a formed in the perpendicular
direction to the plane of paper is specified as the number n in the
perpendicular direction to the plane of paper; whereas the number
of elution holes 12b formed along the longitudinal direction in
parallel to the plane of paper is specified as the number n along
the longitudinal direction in parallel to the plane of paper.
[0058] As shown in FIG. 2, assuming that the distance between the
reinforcing core materials 10 adjacent to each other is represented
by a, the distance between the reinforcing core materials 10 and
the elution holes 12 adjacent to each other is represented by b,
the distance between the elution holes 12 adjacent to each other is
represented by c, and the number of the elution holes 12 formed
between the reinforcing core materials 10 adjacent to each other is
represented by n, then a, b, c, and n satisfying the relationship
represented by the following expression (1) or expression (2) are
at least present.
b>a/(n+1) (1)
c>a/(n+1) (2)
[0059] In the expressions, a/(n+1) corresponds to the distance
between elution holes when they are arranged at equal intervals
between the reinforcing core materials 10. In the interval between
the reinforcing core materials 10 where a, b, c and n satisfying
the relationship represented by expression (1) are present, the
distance b between the reinforcing core materials 10 and the
elution holes 12 adjacent to each other is larger than the equal
intervals (a/(n+1)). In this case, as the distance b between the
reinforcing core materials 10 and the elution holes 12 adjacent to
each other, there are two distances between the adjacent
reinforcing core materials 10, that is, there are two b (more
specifically, in FIG. 2, one is present between the reinforcing
core material 10 on the left and the elution hole 12 and the other
is present between the reinforcing core material 10 on the right
and the elution hole 12). In the present embodiment, it is
satisfactory if at least one of the two b satisfies the
relationship of expression (1). More preferably, the two b present
between the adjacent reinforcing core materials 10 both satisfy the
relationship of expression (1). Note that, a is the sum of all b
and all c present between the reinforcing core materials adjacent
to each other, although it is apparent from the definition.
[0060] In the interval between the reinforcing core materials 10
where a, b, c and n satisfying the relationship represented by
expression (2) are present, the interval c between the elution
holes 12 adjacent to each other is larger than the equal intervals
(a/(n+1)). In this case, as the distance c between the elution
holes 12 adjacent to each other, there are two or more distances c,
if n=3 or more. That is, there are two or more c. In this case, it
is satisfactory if at least one of c satisfies the relationship of
expression (2) in the present embodiment.
[0061] As is apparent from the description above, in the cation
exchange membrane 1 of the present embodiment, it is satisfactory
if at least one arrangement satisfying the relationship of
expression (1) or expression (2).
[0062] Furthermore, the elution holes 12 are preferably arranged at
positions approximately symmetric to the middle of the adjacent
reinforcing core materials. At this time, the two b present between
the adjacent reinforcing core materials become a approximately
equal value.
[0063] If the reinforcing core materials 10 and the elution holes
12 are formed in the membrane body 14 so as to satisfy the
relationship of expression (1) or expression (2), at least the
mechanical strength of the cation exchange membrane 1 can be
improved. By setting positional relationship between the
reinforcing core materials 10 and the elution holes 12 to a
specific positional relationship represented by expression (1) or
expression (2), even if the case where the cation exchange membrane
1 may be fold in handing, a failure such as formation of a pinhole
caused by application of excessive load to a specific site can be
prevented. As a result, the folding resistance of the cation
exchange membrane 1 can be excessively improved; excellent
mechanical strength can be maintained for a long time; and a stable
electrolytic performance can be delivered. In the present
embodiment, as long as either one of expression (1) and expression
(2) is satisfied, the aforementioned effect can be obtained,
however in view of mechanical strength, the relationship of
expression (2) is more preferably satisfied.
[0064] In addition, electrolysis voltage can be further reduced by
satisfying expression (1) or expression (2). Electrolysis voltage
can be reduced by controlling the arrangement of the elution holes
12 to ensure mobility of a cation such as an alkali ion generated
in electrolysis and an electrolyte. A method for controlling the
arrangement of the elution holes 12 may include, for example, a
method of appropriately modifying weaving conditions in a step of
producing a cation exchange membrane, as described later.
[0065] Furthermore, when the cation exchange membrane 1 is
installed within the electrolysis vessel, even if the cation
exchange membrane 1 is rubbed against the electrode, etc. by e.g.,
vibration of the electrolysis vessel, it is possible to prevent the
reinforcing core material 10 from damaging and sticking out through
the surface of the membrane body 14. Since the reinforcing core
material 10, etc. is embedded in the interior portion of the
membrane body, the reinforcing core material 10 would not damage or
stick out through the surface of the membrane body. Particularly,
e.g., local peel off of the reinforcing core material 10 can be
effectively prevented. In this manner, the cation exchange membrane
1 having a long life can be obtained.
[0066] In one aspect of the present embodiments, a, c and n
preferably further satisfy the relationship of the following
expression (3) in addition to the relationship of expression (1) or
expression (2).
0.2a/(n+1).ltoreq.c.ltoreq.0.9a/(n+1) (3)
[0067] By satisfying the relationship of expression (3), the
mechanical strength of the cation exchange membrane 1 can be
further improved. In addition, the effect of reducing electrolysis
voltage can be further improved.
[0068] It is more preferable that a, c and n further satisfy the
relationship of expression (3-1) in addition to the relationship of
expression (1) or expression (2) and further preferable that a, c
and n further satisfy the relationship of expression (3-2).
0.4a/(n+1).ltoreq.c.ltoreq.0.8a/(n-1) (3-1)
0.4a/(n+1).ltoreq.c.ltoreq.0.75a/(n+1) (3-2)
[0069] Furthermore, when the relationship of expression (3) is
satisfied, a, b and n preferably further satisfy the relationship
of the following expression (4)
a/(n+1)<b.ltoreq.1.8a/(n+1) (4)
[0070] By further satisfying the relationship of expression (4) in
addition to expression (3), the mechanical strength of the cation
exchange membrane 1 can be further improved. In addition,
electrolysis voltage can be further reduced.
[0071] In addition to expression (3), a, b and n more preferably
satisfy the relationship of expression (4-1) and further preferably
satisfy the relationship of expression (4-2).
1.05a/(n+1).ltoreq.b.ltoreq.1.6a/(n+1) (4-1)
1.1a/(n+1).ltoreq.b.ltoreq.1.5a/(n+1) (4-2)
[0072] Note that, in the interval between the reinforcing core
materials satisfying the relationships of expression (3) and
expression (4), the interval b between the elution holes and the
reinforcing core materials adjacent to each other is broad and the
interval c between the elution holes is narrow. That is, needless
to say, expression (1) is satisfied between the reinforcing core
materials.
[0073] In addition, as the distance b between the reinforcing core
materials 10 and the elution holes 12 adjacent to each other, there
are two distances between the adjacent reinforcing core materials
10 (more specifically, in FIG. 2, one is present between the left
end reinforcing core material 10 and the elution holes 12 and the
other is present between the right end reinforcing core material 10
and the elution holes 12). Of the two b, at least one b may satisfy
the relationship of expression (4). More preferably, both two b
present between the adjacent reinforcing core materials 10 satisfy
the relationship of expression (4).
[0074] In another embodiment, a, c and n preferably further satisfy
the relationship of the following expression (5) in addition to the
relationship of expression (1) or expression (2).
1.1a/(n+1).ltoreq.c.ltoreq.0.8a (5)
[0075] By satisfying the relationship of expression (5), the
mechanical strength of the cation exchange membrane 1 can be
further improved. By satisfying the relationship of expression (5),
reduction of the tensile elongation of the cation exchange membrane
1 due to folding, etc. can be further suppressed to further reduce
electrolysis voltage.
[0076] More preferably, a, c and n satisfy the relationship of
expression (5-1) in addition to the relationship of expression (1)
or expression (2), and further preferably satisfy the relationship
of expression (5-2).
1.1a/(n+1).ltoreq.c.ltoreq.1.8a/(n+1) (5-1)
1.1a/(n+1).ltoreq.c.ltoreq.1.7a/(n+1) (5-2)
[0077] In the expressions, taking the case where n=2 as an example,
the relationship of the aforementioned expressions will be
described. When n=2, the number of elution holes between the
reinforcing core materials is 2 and intervals are a/(n+1)=a/3 when
elution holes are arranged at equal intervals. Therefore, when n=2,
expression (1) and expression (2) become respectively the following
expression (6) and expression (7).
n=2,b>a/3 (6)
n=2,c>a/3 (7)
[0078] Then, the intervals between the reinforcing core materials
satisfying the relationship of expression (6) preferably further
satisfy the relationship of expression (3). When the relationship
of expression (3) is also satisfied in addition to expression (6),
the interval between elution holes becomes narrow and the interval
between the reinforcing core material and the elution hole becomes
wide. In this manner, mechanical strength improves and electrolysis
voltage can be reduced. More preferably, expression (4) is also
satisfied in addition to expression (1).
[0079] Furthermore, the intervals between the reinforcing core
materials satisfying the relationship of expression (7) preferably
further satisfy the relationship of expression (5). When the
relationship of expression (5) is satisfied in addition to
expression (7), the interval between elution holes becomes wide and
the each interval between the reinforcing core material and the
elution hole becomes narrow. In this manner, mechanical strength
improves and electrolysis voltage can be reduced.
[0080] More preferably, the first interval between the reinforcing
core materials satisfying the relationships of expression (6) and
expression (3) and the second interval between the reinforcing core
materials satisfying the relationships of expression (7) and
expression (5) are arranged alternately and repeatedly. In this
arrangement, mechanical strength is further improved and
electrolysis voltage can be reduced.
[0081] The cation exchange membrane according to the present
embodiment is satisfactory as long as the relationship of
expression (1) or expression (2) is satisfied in a predetermined
direction of the membrane. More specifically, it is satisfactory as
long as the relationship of expression (1) or expression (2) is
satisfied in the direction of at least either one of the MD
direction and the TD direction of the cation exchange membrane. At
least in the TD direction (TD yarn described later) of the cation
exchange membrane, it is preferable to satisfy the relationship of
expression (1) or expression (2), and more preferably both in the
MD direction and in the TD direction of the cation exchange
membrane, the relationship of expression (1) or expression (2) is
satisfied.
[0082] Then, in the direction of at least either one of the MD
direction and the TD direction, it is preferable to have the
intervals between the reinforcing core materials satisfying the
relationships of expression (3) and (4) in addition to the
relationship of expression (1) or expression (2); more preferable
to have the intervals between the reinforcing core materials
further satisfying the relationship of expression (3) at least in
the TD direction (TD yarn) of the cation exchange membrane; and
further preferable to have the intervals between the reinforcing
core materials further satisfying the relationship of expression
(3) both in the MD direction and in the TD direction of the cation
exchange membrane.
[0083] Furthermore, in the direction of at least either one of the
MD direction and the TD direction, it is preferable to have the
intervals between the reinforcing core materials satisfying the
relationship of expression (5), in addition to expression (1) or
expression (2); more preferable to have the intervals between the
reinforcing core materials further satisfying the relationship of
expression (5) at least in the TD direction (TD yarn) of the cation
exchange membrane; and further preferable to have the intervals
between the reinforcing core materials further satisfying the
relationship of expression (5) both in the MD direction and in the
TD direction of the cation exchange membrane.
[0084] The MD direction (machine direction) used herein refers to
the direction along which the membrane body and various core
materials (for example, a reinforcing material obtained in the case
where the reinforcing material is woven by using a reinforcing core
material, a reinforcing yarn, a sacrifice yarn, a dummy yarn, etc.)
are transported ("feed direction") in the process for producing the
cation exchange membrane as described later. Furthermore, the MD
yarn refers to a yarn woven (knitted) along the MD direction. The
TD direction (transverse direction) refers to the direction in
generally perpendicular to the MD direction. Furthermore, the TD
yarn refers to a yarn woven (knitted) along the TD direction. If
not only the relationship of expression (1) or expression (2) but
also expression (3) or expression (5) etc., is satisfied in two
directions, i.e., the MD direction and the TD direction of the
cation exchange membrane, mechanical strength of the cation
exchange membrane can be further improved and electrolysis voltage
can be further reduced.
[0085] FIG. 3 is a conceptual diagram of the second embodiment of
the cation exchange membrane according to the present embodiment. A
cation exchange membrane 2 satisfies the relationship of expression
(1) or expression (2) both in the MD direction and in the TD
direction. More specifically, the cation exchange membrane 2 at
least has two or more reinforcing core materials 20x arranged
within the membrane body in the MD direction (see X) of the
membrane body (not shown) and two or more elution holes 22x are
formed between the reinforcing core materials 20x adjacent to each
other. Assuming that the distance between the reinforcing core
materials 20x adjacent to each other is represented by a.sub.x, the
distance between the reinforcing core materials 20x and the elution
holes 22x adjacent to each other is represented by b.sub.x, the
distance between the elution holes 12 adjacent to each other is
represented by c.sub.x, and the number of the elution holes 22x
formed between the reinforcing core materials 20x adjacent to each
other is represented by n.sub.x, then the relationship represented
by the following expression (1.times.) or expression (2.times.) is
satisfied.
b.sub.x>a.sub.x/(n.sub.x+1) (1.times.)
c.sub.x>a.sub.x/(n.sub.x+1) (2.times.)
[0086] Furthermore, the cation exchange membrane 2 has at least two
or more reinforcing core materials 20y arranged within the membrane
body in the TD direction (see Y) of the membrane body (not shown)
and two or more elution holes 22y are formed between the
reinforcing core materials 20y adjacent to each other. Assuming
that the distance between the reinforcing core materials 20y
adjacent to each other is represented by a.sub.y, the distance
between the reinforcing core materials 20y and the elution holes
22y adjacent to each other is represented by b.sub.y, the distance
between the adjacent elution holes 12 is represented by c.sub.y,
and the number of the elution holes 22y formed between the adjacent
reinforcing core materials 20y is represented by n.sub.y, then the
relationship represented by the following expression (1y) or
expression (2y) is satisfied.
b.sub.y>a.sub.y/(n.sub.y+1) (1y)
c.sub.y>a.sub.y/(n.sub.y+1) (2y)
[0087] In the present embodiment, it is not necessary that all
reinforcing core materials and elution holes in the cation exchange
membrane are formed so as to satisfy the aforementioned specific
relationship (for example, expression (1) or expression (2), or
expression (3) or expression (5) or the like). For example, if the
cation exchange membrane has at least one interval between the
reinforcing core materials having elution holes arranged so as to
satisfy the relationship of expression (1) or expression (2),
folding resistance of the cation exchange membrane is improved.
[0088] Furthermore, assuming that the region partitioned by
adjacent two reinforcing core materials in the MD direction of the
cation exchange membrane and adjacent two reinforcing core
materials in the TD direction thereof is specified as one region,
the ratio of the area of regions satisfying the relationship of
expression (1) or expression (2) relative to the area of all
regions in the cation exchange membrane is not particularly
limited; however, it is preferably from 80 to 100% and more
preferably from 90 to 100%. The edge periphery of the cation
exchange membrane is to be immobilized in the electrolysis vessel
while using and used as a site sandwiched by e.g., flanges of the
electrolysis vessel. If the area ratio is 80% or more, in a portion
corresponding to a current-carrying portion, formation of e.g.,
pinholes and cracks by folding can be prevented. For this reason,
the area ratio of 80% or more is preferable. In addition, if the
area ratio is 80% or more, in the portion corresponding to a
current-carrying portion, an effect of reducing electrolysis
voltage can be obtained. For this reason, the area ratio of 80% or
more is preferable.
[0089] Furthermore, when the relationship of expression (3) or
expression (5) is satisfied, the area ratio of regions satisfying
the relationship of expression (3) or expression (5) is not
particularly limited; however, it is preferably from 40 to 100%
relative to the area of all regions in the cation exchange membrane
and more preferably from 45 to 100%. In the region satisfying the
relationship of expression (3) or expression (5), folding
resistance tends to be further superior, compared to the region
also satisfying expression (1) or expression (2). Therefore, if the
area ratio is 40% or more, sufficiently high folding resistance can
be obtained.
[0090] FIG. 4 is a conceptual diagram of the third embodiment of
the cation exchange membrane according to the present embodiment. A
cation exchange membrane 3 is a cation exchange membrane at least
having a membrane body (not shown) containing a fluorine-based
polymer having an ion-exchange group and two or more reinforcing
core materials 301, 302, 303 arranged approximately in parallel
within the membrane body, and 2 sets or more n number of elution
holes 321, 322, 323, . . . , 324, 325, 326, . . . are formed
between the reinforcing core materials adjacent to each other.
[0091] In the case of FIG. 4, the interval between the reinforcing
core materials separated by the reinforcing core materials 301 and
302 and the interval between the reinforcing core materials
separated by the reinforcing core materials 302 and 303 are
arranged alternately and repeatedly. More specifically, in the
interval between the reinforcing core materials separated by the
reinforcing core materials 301 and 302, the elution holes 321, 322,
323 are formed at the distance c.sub.1, c.sub.2, . . . (hereinafter
sometimes collectively referred to as c). Of these, at least
c.sub.1 satisfies the relationship of expression (2):
c.sub.1>a.sub.1/(n+1). In contrast, in the interval between the
reinforcing core materials separated by the reinforcing core
materials 302 and 303, the interval b.sub.2 between the reinforcing
core materials and the elution holes adjacent to each other at
least satisfies the relationship of expression (1):
b.sub.2>a.sub.1/(n+1).
[0092] As described above, in the cation exchange membrane, it is
preferable that the first interval between the reinforcing core
materials (the interval separated by the reinforcing core material
302 and the reinforcing core material 303) satisfying the
relationship of expression (1) and the second interval between the
reinforcing core materials (the interval separated by the
reinforcing core material 301 and the reinforcing core material
302) satisfying the relationship of expression (2) alternately
appear. Owing to this arrangement, mechanical strength of the
cation exchange membrane 3 can be further improved in the direction
and electrolysis voltage thereof can be further reduced.
[0093] Note that, in the present embodiment, the direction along
which the first region and the second region above are alternately
arranged in the cation exchange membrane is not particularly
limited; however, in at least either the MD direction or the TD
direction of the cation exchange membrane, the first interval
between the reinforcing core materials satisfying the relationship
of expression (1) and the second interval between the reinforcing
core materials satisfying the relationship of expression (2) are
alternately arranged. The cation exchange membrane having such
arrangement is preferable. More preferably, the cation exchange
membrane has the first interval between the reinforcing core
materials satisfying the relationship of expression (1) and the
second interval between the reinforcing core materials satisfying
the relationship of expression (2), which are alternately and
repeatedly arranged along the MD direction (TD yarn arrangement
direction) of the cation exchange membrane. Further preferably, the
cation exchange membrane has the first interval between the
reinforcing core materials satisfying the relationship of
expression (1) and the second interval between the reinforcing core
materials satisfying the relationship of expression (2), which are
alternately and repeatedly arranged along the MD direction and the
TD direction.
[0094] Generally, the cation exchange membrane has a rectangular
shape. In most cases, its longitudinal direction corresponds to the
MD direction and its transverse direction corresponds to the TD
direction. Such the cation exchange membrane is wound around a
tubular body like a vinyl chloride tube to transport at the time of
shipment and during a lead time until installation into an
electrolysis vessel. When the membrane is wound around the tubular
body, the cation exchange membrane is sometimes folded in the TD
direction to reduce the length of the tubular body. Even in such
the case, concentration of load in the TD direction can be
efficiently avoided as long as the cation exchange membrane
contained as mentioned above is used, and thus formation of a
pinhole, etc., can be effectively prevented.
[0095] As one aspect of the present embodiments, the cation
exchange membrane preferably has the first interval between the
reinforcing core materials satisfying the relationship of
expression (1), which further satisfies the relationships of
expressions (3) and (4) and the second interval between the
reinforcing core materials satisfying the relationship of
expression (2), which further satisfies the relationship of
expression (5). Owing to this arrangement, mechanical strength can
be further improved and electrolysis voltage can be further
reduced. Note that, even in this case, the direction along which
the first region and the second region above are alternately
arranged in the cation exchange membrane is not particularly
limited.
[0096] Furthermore, as another embodiment, the ion exchange
membrane preferably has the first interval between the reinforcing
core materials satisfying the relationship of expression (1) which
further satisfies the relationship of expression (6) and the second
interval between the reinforcing core materials satisfying the
relationship of expression (2) which further satisfies the
relationship of expression (7). Owing to this arrangement,
mechanical strength can be further improved and electrolysis
voltage can be further reduced. Note that, even in this case, the
direction along which the first region and the second region above
are alternately arranged in the cation exchange membrane is not
particularly limited.
[0097] FIG. 5 is a conceptual diagram of the fourth embodiment of
the cation exchange membrane according to the present embodiment. A
cation exchange membrane 4 is a cation exchange membrane at least
having a membrane body (not shown) containing a fluorine-based
polymer having an ion-exchange group and two or more reinforcing
core materials 401, 402, 403 arranged approximately in parallel
within the membrane body, in which, in at least either one of the
directions, i.e., in the MD direction or in the TD direction, of
the cation exchange membrane 4, the interval between the
reinforcing core materials satisfying the relationship of the
following expression (6) and the interval between the reinforcing
core materials satisfying the relationship of the following
expression (7) are alternately present.
n=2,b>a/3 (6)
n=2,c>a/3 (7)
[0098] Such an arrangement is preferable because mechanical
strength can be further improved and electrolysis voltage can be
further reduced by the arrangement.
[0099] In FIG. 5, in the interval separated by the reinforcing core
material 401 and the reinforcing core material 402, the distance
b.sub.1 between the reinforcing core material 401 and the elution
hole 421 and the distance b.sub.2 between the reinforcing core
material 402 and the elution hole 422 both satisfy the relationship
of the above expression (6): b.sub.1 (b.sub.2)>a/3. Furthermore,
the distance c.sub.1 between two elution holes 421 and 422
satisfies the relationship: c.sub.1<a.sub.1/3. In other words,
in the interval separated by the reinforcing core material 401 and
the reinforcing core material 402, the distance c.sub.1 between two
elution holes 421 and 422 is narrow compared to the distance
between them in which they are arranged at an equal interval.
[0100] Note that, in the expression (6), it is satisfactory if at
least either one of b.sub.1 or b.sub.2 satisfies the relationship
of b>a/3, however in view of mechanical strength and convenience
in production, it is more preferable that b.sub.1 and b.sub.2 both
satisfy the relationship: b>a/3.
[0101] In the interval separated by the reinforcing core material
402 and the reinforcing core material 403, the distance b.sub.3
between the reinforcing core material 402 and the elution hole 423
and the distance b.sub.4 between the reinforcing core material 403
and the elution hole 434 both satisfy the relationship:
b<a.sub.2/3. Furthermore, the distance c.sub.2 between two
elution holes 423 and 424 satisfies the relationship of the
expression (7): c.sub.2>a.sub.2/3. In other words, in the
interval separated by the reinforcing core material 402 and the
reinforcing core material 403, the distance c.sub.2 between two
elution holes 423 and 424 is wide compared to the distance between
them in which they are arranged at an equal interval.
[0102] Note that, if the relationship of expression (7) above is
satisfied, at least either one of b.sub.3 or b.sub.4 may satisfy
the relationship: b<a/3; however, it is preferable that, in view
of mechanical strength and convenience in production, b.sub.3 and
b.sub.4 both satisfy the relationship: b<a/3.
[0103] In at least either one of the directions, i.e., the MD
direction or the TD direction of the cation exchange membrane 4, it
is more preferable that the interval between reinforcing core
materials satisfying the relationship of the following expression
(8) and the interval between reinforcing core materials satisfying
the relationship of the following expression (9) are alternately
present. In this case, in FIG. 5, distances a.sub.1, b.sub.1,
b.sub.2, and c.sub.1 satisfy the relationship of the following
expression (8); and distances a.sub.2, b.sub.3, b.sub.4, and
c.sub.2 satisfy the relationship of the following expression
(9).
n=2,0.2a/3.ltoreq.c.ltoreq.0.9a/3,a/3<b.ltoreq.1.8a/3 (8)
n=2,1.1a/3.ltoreq.c.ltoreq.0.8 (9)
[0104] Owing to this arrangement, mechanical strength can be
further improved and electrolysis voltage can be further
reduced.
[0105] FIG. 6 is a conceptual diagram of the fifth embodiment of
the cation exchange membrane according to the present embodiment.
In a cation exchange membrane 5, 4 regions are formed, which are
partitioned by reinforcing core materials 501x, 502x, 503x arranged
along the MD direction (see X) and reinforcing core materials 501y,
502y, 503y arranged along the TD direction (see Y). Furthermore,
elution holes 521x, 522x, 523x, 524x are formed along the MD
direction of the cation exchange membrane 5 and elution holes 521y,
522y, 523y, 524y are formed along the TD direction. Moreover, the
cation exchange membrane 5 has a structure having a region where
the intervals between elution holes are less densely arranged and a
region where the intervals between elution holes are densely
arranged are alternately arranged in both the MD direction and in
the TD direction.
[0106] The cation exchange membrane 5 has (i) a first region
surrounded by the reinforcing core materials 501x, 502x in the MD
direction and the reinforcing core materials 501y, 502y in the TD
direction, (ii) a second region surrounded by the reinforcing core
materials 502x, 503x in the MD direction and the reinforcing core
materials 501y, 502y in the TD direction; (iii) a third region
surrounded by the reinforcing core materials 502x, 503x in the MD
direction and the reinforcing core materials 501y, 502y in the TD
direction and (iv) a fourth region surrounded by the reinforcing
core materials 502x, 503x in the MD direction and the reinforcing
core materials 502y, 503y in the TD direction. These regions are
repeatedly arranged.
[0107] In the first region, the elution holes 521x, 522x are
arranged in the MD direction so as to satisfy the relationship of
expression (6) and the elution holes 521y, 522y are arranged in the
TD direction so as to satisfy the relationship of expression (7).
Since mechanical strength can be further improved and electrolysis
voltage can be further reduced, the elution holes 521x, 522x are
preferably arranged in the MD direction so as to satisfy the
relationship of expression (8). Owing to this arrangement,
mechanical strength of the cation exchange membrane can be further
improved and electrolysis voltage thereof can be further reduced.
Similarly, the elution holes 521y, 522y are preferably arranged in
the TD direction so as to satisfy the relationship of expression
(9).
[0108] In the second region, the elution holes 523x, 524x are
arranged in the MD direction so as to satisfy the relationship of
expression (7) and the elution holes 521y, 522y are arranged in the
TD direction so as to satisfy the relationship of expression (7).
In the MD direction, the elution holes 523x, 524x are preferably
arranged so as to satisfy the relationship of expression (9). Owing
to this arrangement, mechanical strength of the cation exchange
membrane can be further improved and electrolysis voltage thereof
can be further reduced. Similarly, the elution holes 521y, 522y are
preferably arranged in the TD direction so as to satisfy the
relationship of expression (9).
[0109] In the third region, the elution holes 521x, 522x are
arranged in the MD direction so as to satisfy the relationship of
expression (6) and the elution holes 523y, 524y are arranged in the
TD direction so as to satisfy the relationship of expression (6).
In the MD direction, the elution holes 521x, 522x are preferably
arranged so as to satisfy the relationship of expression (8). Owing
to this arrangement, mechanical strength of the cation exchange
membrane can be further improved and electrolysis voltage thereof
can be further reduced. Similarly, the elution holes 523y, 524y are
preferably arranged in the TD direction so as to satisfy the
relationship of expression (8).
[0110] In the fourth region, the elution holes 523x, 524x are
arranged in the MD direction so as to satisfy the relationship of
expression (7) and the elution holes 523y, 524y are arranged in the
TD direction so as to satisfy the relationship of expression (6).
In the MD direction, the elution holes 523x, 524x are preferably
arranged so as to satisfy the relationship of expression (9). Owing
to this arrangement, mechanical strength of the cation exchange
membrane can be further improved and electrolysis voltage thereof
can be further reduced. Similarly, the elution holes 523y, 524y are
preferably arranged in the TD direction so as to satisfy the
relationship of expression (8).
[0111] Owing to the aforementioned structure, balance of
arrangement of the reinforcing core materials and the elution holes
in the cation exchange membrane can be further improved, with the
result that the dimensional stability can be further improved.
<Producing Method>
[0112] A method for producing a cation exchange membrane according
to the present embodiment, comprising the steps of:
[0113] weaving two or more reinforcing core materials, a sacrifice
yarn soluble in an acid or an alkali, and a dummy yarn having a
property of dissolving in a predetermined solvent in which the
reinforcing core materials and the sacrifice yarn are insoluble, to
obtain a reinforcing material having the sacrifice yarn and the
dummy yarn arranged between the reinforcing core materials adjacent
to each other;
[0114] soaking the reinforcing material in the predetermined
solvent to remove the dummy yarn from the reinforcing material;
[0115] stacking the reinforcing material from which the dummy yarn
is removed and a fluorine-based polymer having an ion-exchange
group or an ion-exchange group precursor which can be converted
into the ion-exchange group by hydrolysis, to form a membrane body
having the reinforcing material; and
[0116] soaking the sacrifice yarn in an acid or an alkali to remove
the sacrifice yarn from the membrane body, thereby forming an
elution hole in the membrane body.
[0117] One of the characteristics of the present embodiment resides
in that the intervals of the elution holes formed between the
reinforcing core materials adjacent to each other (see, for
example, FIG. 2 b, c) are not equally separated. In order to easily
and efficiently realize such the structure, a dummy yarn can be
used. This will be more specifically described with reference to
FIG. 7.
[0118] FIG. 7 is a conceptual diagram for illustrating a producing
method according to the present embodiment. First, between two or
more reinforcing core materials 60, sacrifice yarns 62 for forming
elution holes and dummy yarns 66 are woven to obtain a reinforcing
material 6 (see FIG. 7, (i)). The reinforcing material 6 can be
obtained as a so-called woven fabric and a knitted fabric etc. Note
that, in view of productivity, a woven fabric is preferable. In
this case, between the reinforcing core materials 60, the sacrifice
yarns 62 and the dummy yarns 66 are preferably woven so as to be
arranged at approximately equal intervals (interval d). By weaving
the sacrifice yarns 62 and the dummy yarns 66 at approximately
equal intervals, no complicated control is required to arrange the
sacrifice yarns 62 at the intervals which satisfy relational
expression of expression (1) and expression (2), etc., and an
operation for weaving yarns can be simply performed with a
satisfactory production efficiency. Note that, the dummy yarn 66
has a high solubility to a predetermined solvent.
[0119] Then, the reinforcing material 6 is soaked in a
predetermined solvent to selectively dissolve and remove the dummy
yarn 66 alone (see FIG. 7 (ii)). Owing to this step, the site where
the dummy yarns 66 have been woven becomes a vacant space and thus
the interval is widened.
[0120] The type of the predetermined solvent for dissolving and
removing the material for the dummy yarn 66 and dummy yarn 66 is
not particularly limited; however, it is satisfactory if the
solubility of the dummy yarn to the predetermined solvent is higher
than that of the reinforcing core material 60 and the sacrifice
yarn 62. Examples of the material for the dummy yarn 66 may include
polyvinyl alcohol (PVA), rayon, polyethylene terephthalate (PET),
cellulose and polyamide. Of these, polyvinyl alcohol is preferable
in view of high solubility.
[0121] As the predetermined solvent, any solvent may be used as
long as it does not dissolve a reinforcing core material and a
sacrifice yarn but can dissolve a dummy yarn. Therefore, the
amount, etc. of solvent required for dissolving the dummy yarn is
not particularly limited; however, the kind and amount of solvent
can be appropriately selected in consideration of the quality of
the reinforcing core material, sacrifice yarn, dummy yarn to be
used and producing conditions, etc. Examples of such a solvent may
include an acid, an alkali and hot water. Examples of the acid may
include hydrochloric acid, nitric acid and sulfuric acid. Examples
of the alkali may include sodium hydroxide and potassium hydroxide.
Of these, sodium hydroxide or hot water is preferable in view of
high dissolution rate.
[0122] The thickness and shape, etc. of the dummy yarn 66 are not
particularly limited; however, a yean formed of from 4 to 12
polyvinyl alcohol filaments having a thickness of from 20 to 50
deniers and a circular cross-section is preferable.
[0123] The sacrifice yarn 62 refers to a yarn capable of dissolving
in an acid or an alkali to form an elution hole in the cation
exchange membrane. In addition, the solubility of the sacrifice
yarn 62 in a predetermined solvent in which the dummy yarn 66
dissolves is lower than that of the dummy yarn 66. Examples of the
material for the sacrifice yarn 62 may include polyvinyl alcohol
(PVA), rayon, polyethylene terephthalate (PET), cellulose and
polyamide. Of these, polyethylene terephthalate (PET) is preferable
in view of stability during a weaving step and solubility to an
acid or an alkali.
[0124] The amount of the sacrifice yarn 62 contained in a fabric is
preferably from 10 to 80 mass % based on the total amount of the
reinforcing material and more preferably from 30 to 70 mass %.
Furthermore, the sacrifice yarn has a thickness of from 20 to 50
deniers and preferably formed of a monofilament or
multifilament.
[0125] The dummy yarn 66 can be woven such that it inserts between
sacrifice yarns 62 and between the reinforcing core material 60 and
the sacrifice yarn 62. Therefore, the intervals of the reinforcing
core materials 60 and the sacrifice yarns 62 arranged in the
reinforcing material 6 can be arbitrarily determined by
appropriately selecting the thickness and shape of the dummy yarn
and the manner and order of weaving the dummy yarn. Since the dummy
yarn 66 is removed by a predetermined solvent before the
reinforcing material 6 is layered on a fluorine-based polymer, the
interval of the sacrifice yarns 62 to be arranged can be
arbitrarily determined. In this manner, the reinforcing core
material 60 and the sacrifice yarn 62 for forming an elution hole
can be arranged so as to satisfy the relationship of expression (1)
or expression (2).
[0126] Furthermore, as to the MD yarn, although not shown in the
figure, the sacrifice yarn, etc. can be arranged at arbitrary
intervals in the reinforcing material by a method of passing a
bundle of two or more yarns selected from the reinforcing yarn, the
sacrifice yarn and the dummy yarn through a single dent of the reed
of the weaving machine or a method of providing a dent having no
yarn between dents through which a reinforcing yarn, a sacrifice
yarn, a dummy yarn, etc. are passed. For example, control in the MD
direction can be made by varying types of yarns (reinforcing yarn,
sacrifice yarn, etc.) used in combination passing through a single
dent of the reed of a weaving machine. More specifically, a bundle
of a reinforcing yarn and a sacrifice yarn is passed through a
first dent, a bundle of a sacrifice yarn and a reinforcing yarn is
passed through a second yarn, a sacrifice yarn and a sacrifice yarn
are passed through a third bundle. In this case, the arrangement of
a reinforcing yarn, a sacrifice yarn, a sacrifice yarn, a
reinforcing yarn, a sacrifice yarn and a sacrifice yarn in this
order can be repeatedly made. In this manner, the intervals of the
sacrifice yarn arranged in a reinforcing material can be
controlled.
[0127] Subsequently, the reinforcing material 6 from which a dummy
yarn 66 is removed is layered on a fluorine-based polymer having an
ion-exchange group to form a membrane body having the reinforcing
material 6. A preferable method for forming the membrane body may
include, for example, a method having the following (1) step and
(2) step.
[0128] (1) A fluorine-based polymer layer (hereinafter referred to
as a "first layer") containing a carboxylate functional group
positioned on the cathode side and a fluorine-based polymer layer
(hereinafter referred to as a "second layer") containing a sulfonyl
fluoride functional group are coextruded to form a film.
Subsequently, the reinforcing material and the second layer/first
layer composite film are layered in this order on a flat-plate or a
drum having a heat source and a vacuum source, and having micro
pores in the surface, via a permeable heat resistant release paper.
These films are integrated at the temperature under which
individual polymers melt while removing air between the layers by
reducing pressure.
[0129] (2) Separately from the second layer/first layer composite
film, a fluorine-based polymer layer (hereinafter referred to as a
"third layer") containing a sulfonyl fluoride functional group is
singly formed into a film in advance. Subsequently, the third layer
film, reinforcing material and second layer/first layer composite
film are layered in this order on a flat-plate or a drum having a
heat source and a vacuum source and having micro pores in the
surface, via a permeable heat resistant release paper. These films
are integrated at the temperature under which individual polymers
melt while removing air between the layers by reducing pressure.
Note that, in this case, the direction along which the extruded
film is fed is the MD direction.
[0130] Coextruding the first layer and the second layer in the step
(1) contributes to enhancing the adhesion strength of the
interface. Furthermore, in the integration method under reduced
pressure, compared to a pressurizing press method, the thickness of
the third layer on the reinforcing material characteristically
increases. Moreover, since the reinforcing material is immobilized
within the cation exchange membrane, mechanical strength of the
cation exchange membrane can be sufficiently maintained.
[0131] Note that, to further increase the durability of the cation
exchange membrane, a layer (hereinafter referred to as a "fourth
layer") containing both a carboxylate functional group and a
sulfonyl fluoride functional group can be further interposed
between the first layer and the second layer and a layer containing
both a carboxylate functional group and a sulfonyl fluoride
functional group can be used as the second layer. In this case, a
method in which a polymer containing a carboxylate functional group
and a polymer containing a sulfonyl fluoride functional group are
separately produced and then mixed, and a method in which a monomer
containing a carboxylate functional group and a monomer containing
a sulfonyl fluoride functional group both are copolymerized and put
in use may be used.
[0132] In the case where the fourth layer is used as a
constitutional element of the cation exchange membrane, the first
layer and the fourth layer may be formed into a coextrusion film,
the second layer and the third layer may be separately and singly
formed into films, and then these films may be layered in
accordance with the aforementioned method. Furthermore, the three
layers, i.e., first layer, fourth layer and second layer, may be
simultaneously coextruded into a film. In this manner, a membrane
body containing a fluorine-based polymer having an ion-exchange
group can be formed on the reinforcing material.
[0133] Furthermore, the sacrifice yarn contained in the membrane
body is removed by dissolving it in an acid or an alkali to form
elution hole(s) in the membrane body. The sacrifice yarn has a
solubility to an acid or an alkali and the sacrifice yarn is eluted
in the cation exchange membrane producing step and under the
electrolysis environment to form elution holes at the elution
sites. In this manner, the cation exchange membrane having elution
holes formed in the membrane body can be obtained. The elution
holes are formed with positional relationship satisfying the
aforementioned relational expression represented by expression (1)
or expression (2).
[0134] Furthermore, the cation exchange membrane according to the
present embodiment preferably has a protruding portion only
consisting of polymer having an ion-exchange group on the sulfonic
acid layer side (on the anode surface side, see FIG. 1). The
protruding portion is preferably consisting of resin alone. The
protruding portion can be formed by previously embossing the
release paper which can be used in integrating the aforementioned
composite film of the second layer and the first layer and the
reinforcing material, etc.
[0135] The cation exchange membrane according to the present
embodiment can be used in various electrolysis vessels. FIG. 10 is
a conceptual diagram of the electrolysis vessel according to the
present embodiment.
An electrolysis vessel A at least has an anode A1, a cathode A2 and
the cation exchange membrane 1 according to the present embodiment
arranged between the anode A1 and the cathode A2. The electrolysis
vessel A can be used for various types of electrolysis.
Hereinbelow, as a typical example, the case where the cation
exchange membrane is used in electrolysis for an aqueous alkali
chloride solution will be described.
[0136] Electrolysis conditions are not particularly limited;
however, electrolysis can be performed in conventionally known
conditions. For example, a 2.5 to 5.5 N aqueous alkali chloride
solution is supplied to an anode chamber, whereas water or a
diluted aqueous alkali hydroxide solution is supplied to a cathode
chamber. Electrolysis can be performed in the conditions: a
temperature of from 50 to 120.degree. C. and a current density of
from 5 to 100 A/dm.sup.2.
[0137] The constitution of the electrolysis vessel according to the
present embodiment is not particularly limited; for example, a
unipolar system or a multipolar system may be employed. The
materials for constituting the electrolysis vessel are not
particularly limited. For example, as a material for the anode
chamber, alkali chloride and chlorine-resistant titanium are
preferable. As a material for the cathode chamber, e.g., alkali
hydroxide and hydrogen-resistant nickel are preferable. As the
arrangement of electrodes, an appropriate interval may be provided
between the cation exchange membrane and the anode. However if the
anode is arranged in contact with the ion exchange membrane, this
structure can be used without any problem. Furthermore, the cathode
is generally arranged at an appropriate interval with the cation
exchange membrane. However, a contact-type electrolysis vessel
(zero-gap system electrolysis vessel) having no interval between
them can be used without any problem.
[0138] In the cation exchange membrane according to the present
embodiment, electrolysis voltage can be reduced by arranging
membrane-constituting members within the membrane body so as to
satisfy the aforementioned relational expressions. Particularly,
compared to a conventional cation exchange membrane where elution
holes for passing various substances such as a cation are arranged
at equal intervals, resistance to a cation decreases by arranging
elution holes at unequal intervals. As a result, electrolysis
voltage may presumably decrease (note that, the function of the
present embodiment is not limited to this).
[0139] Particularly, in the intervals between reinforcing core
materials satisfying the relationship of aforementioned expression
(2), elution holes are arranged near a reinforcing core material
interrupting a cation. Owing to the arrangement, the region
interrupting a cation reduces and the resistance to a cation
further reduces. As a result, electrolysis voltage is further
reduced (note that, the function of the present embodiment is not
limited to this).
EXAMPLES
[0140] Hereinbelow, the present invention will be more specifically
described by way of Examples. Note that, the present invention is
not limited to the following Examples.
[Measurement of Distance]
[0141] The distance a between the reinforcing core materials
adjacent to each other, distance b (b.sub.1, b.sub.2) between the
reinforcing core materials and elution holes adjacent to each
other, and the distance c (c.sub.1, c.sub.2) between the elution
holes adjacent to each other were measured by the following methods
(see FIGS. 8 and 9).
[0142] In the case where the distance in the TD direction was
measured, the cation exchange membrane was cut along the direction
in perpendicular to the TD direction (i.e., the MD direction). The
cut surface was a cross section of the cation exchange membrane in
the TD direction. In the case where the distance in the MD
direction was measured, the cation exchange membrane was cut along
the direction in perpendicular to the MD direction (the TD
direction). The cut surface was a cross section of the cation
exchange membrane in the MD direction.
[0143] The cross section of the cation exchange membrane was
magnified by a microscope and a, b and c in the TD direction and in
the MD direction were measured. At this time, the distance was
determined by measuring the distance between the center point of
the reinforcing core material and the center point of the elution
hole in the transverse direction. For example, a was determined by
measuring the distance between the center point of the reinforcing
core material and the center point of the other adjacent
reinforcing core material in the transverse direction. Note that,
a, b and c were measured 5 times and an average value of the 5
measurement values was used.
[Measurement of Folding Resistance]
[0144] Degree of reduction in strength (folding resistance) by
folding the cation exchange membrane was evaluated by the following
method. Note that, the folding resistance refers to the ratio of
the tensile elongation (tensile elongation ratio) of the cation
exchange membrane after folding relative to the tensile elongation
of the cation exchange membrane before folding.
[0145] Tensile elongation was measured by the following method. A
sample of 1 cm in width was cut along the direction having an angle
of 45 degrees against the reinforcing yarn embedded in the cation
exchange membrane. Subsequently, the tensile elongation of the
sample was measured in the conditions: the distance between chucks:
50 mm, a tension rate: 100 mm/minute in accordance with JIS
K6732.
[0146] The cation exchange membrane was folded by the following
method. The cation exchange membrane was folded by applying weight
of 400 g/cm.sup.2 so as to allow the surface of the carboxylic acid
layer side (see FIG. 1, the carboxylic acid layer 144, and "polymer
A layer" described later) to face inside. In the MD-folding, the
cation exchange membrane was folded so as to form a folding line in
perpendicular to the MD yarn of the cation exchange membrane and
evaluation was made (MD folding). In the TD folding, the cation
exchange membrane was folded so as to form a folding line in
perpendicular to the TD yarn of the cation exchange membrane and
evaluation was made (TD folding). Therefore, in the MD folding,
contribution of control of intervals between reinforcing core
materials and elution holes arranged along the TD direction to
folding resistance can be evaluated, whereas in the TD folding,
contribution of control of intervals between reinforcing core
materials and elution holes arranged along the MD direction to
folding resistance can be evaluated.
[0147] After MD folding and TD folding were separately made,
tensile elongation of the cation exchange membrane was measured to
obtain a ratio of tensile elongation relative to that before
folding. This ratio was employed as a folding resistance.
[Measurement of Electrolysis Voltage]
[0148] An electrolysis vessel was prepared using the cation
exchange membrane and its electrolysis voltage was measured. The
electrolysis voltage was measured in an electrolysis cell of a
forced circulation type having a 1.5 mm-gap. As the cathode, an
electrode formed by applying nickel oxide serving as a catalyst
onto a nickel expanded metal was used. As the anode, an electrode
formed by applying ruthenium, iridium and titanium serving as a
catalyst onto a titanium expanded metal was used. In the
electrolysis cell, the cation exchange membrane was arranged
between the anode chamber and the cathode chamber.
[0149] To the anode side, an aqueous sodium chloride solution was
supplied while controlling a concentration to be 205 g/L, whereas
water was supplied while maintaining the caustic soda concentration
on the cathode side at 32 wt %. Subsequently, electrolysis was
performed for 7 days at a current density of 80 A/dm.sup.2 and a
temperature of 90.degree. C., in the conditions that liquid
pressure on the cathode side of the electrolysis vessel was set to
be higher by 5.3 kPa than the liquid pressure of the anode side.
Thereafter, the electrolysis voltage required was measured by a
voltmeter.
Example 1
[0150] As a reinforcing core material, a monofilament of
polytetrafluoroethylene (PTFE) of 90 deniers (hereinafter referred
to as a "PTFE yarn") was used. As a sacrifice yarn, a yarn of
6-filament polyethylene terephthalate (PET) of 40 deniers twisted
at a rate of 200 times/m (hereinafter referred to as a "PET yarn")
was used. As a dummy yarn, a yarn of 15-filament polyvinyl alcohol
(PVA) of 36 deniers twisted at a rate of 200 times/m (hereinafter
referred to as a "PVA yarn") was used.
[0151] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 3-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PTFE yarn was passed through
a second reed; and a bundle of 2 yarns consisting of PET yarn and
PET yarn was passed through a third reed. The bundles of yarns in
this combination were sequentially and repeatedly passed through
the reed in this order. As to TD yarns, PTFE yarn, PET yarn, PVA
yarn, PVA yarn, PET yarn, PTFE yarn, PVA yarn, PVA yarn, PET yarn,
PET yarn, PVA yarn and PVA yarn were arranged in this order
repeatedly and at approximately equal intervals to obtain a plain
weave. In this manner, a woven fabric (reinforcing material) was
obtained. Subsequently, the obtained reinforcing material was
subjected to contact bonding performed by a roll heated to
125.degree. C. Thereafter, the reinforcing material was soaked in a
0.1 N aqueous sodium hydroxide solution to dissolve a dummy yarn
(PVA yarn) alone and remove it from the reinforcing material. The
thickness of the reinforcing material from which the dummy yarn was
removed was 81 .mu.m.
[0152] Next, dry-resin polymer A, which was a copolymer of
tetrafluoroethylene (CF.sub.2.dbd.CF.sub.2) and
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2COOCH.sub.3
and had a total ion exchange capacity of 0.85 mg equivalent/g, and
a dry-resin polymer B, which was a copolymer of
CF.sub.2.dbd.CF.sub.2 and
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2SO.sub.2F and
had a total ion exchange capacity of 1.05 mg equivalent/g, were
prepared. Using polymers A and B, two-layered film X, which
consisted of a polymer A layer of 13 .mu.m in thickness and a
polymer B layer of 84 .mu.m in thickness, was obtained in
accordance with a coextrusion T-die method. Furthermore, film Y
consisting of a polymer B of 20 .mu.m in thickness was obtained by
using a single layer T-die method.
[0153] Subsequently, release paper, film Y, a reinforcing material
and film X were layered in this order on a drum housing a heat
source and a vacuum source and having micro pores in the surface,
and heated under reduced pressure. At this time, the processing
temperature was 219.degree. C. and a degree of pressure reduction
was 0.022 MPa. Thereafter, the release paper was removed to obtain
composite film. The obtained composite film was soaked in an
aqueous solution containing 30 mass % of dimethyl sulfoxide (DMSO)
and 15 mass % of potassium hydroxide (KOH) at 90.degree. C. for 1
hour to perform hydrolysis, followed by washing with water and
drying. In this manner, the sacrifice yarn (PET yarn) was dissolved
to obtain a membrane body having elution holes formed therein.
[0154] Furthermore, to a 5 mass % ethanol solution of an acid-type
polymer, polymer B, zirconium oxide having a primary particle size
of 1 .mu.m was added up to a faction of 20 mass .degree. A), and
dispersed to prepare a suspension solution. The suspension solution
was sprayed to both surfaces of the above composite film by a spray
method and dried to form a coating layer (0.5 mg/cm.sup.2) on the
surfaces of the composite film. In this manner, the cation exchange
membrane 7 as shown in FIG. 8 was obtained. The cation exchange
membrane 7 of FIG. 8 had a membrane body (not shown) and two or
more reinforcing core materials 70 arranged approximately in
parallel within the membrane body. The membrane body had a
structure where two elution holes 72 were formed between the
reinforcing core materials 70 adjacent to each other. In the
structure of Example 1, the intervals between reinforcing core
materials having a.sub.1, b.sub.1, c.sub.1 and the intervals
between reinforcing core materials having a.sub.2, b.sub.2, c.sub.2
repeatedly appear in the TD direction or in the MD direction. Note
that, in other Examples and Comparative Examples described later,
if the intervals between reinforcing core materials have only
single a, b, c values in the TD direction or in the MD direction,
these values will be hereinafter described as a.sub.1, b.sub.1,
c.sub.1.
[0155] In the obtained cation exchange membrane, in the TD
direction, the distance a.sub.2 between the reinforcing core
materials adjacent to each other was 1112 .mu.m, the number n of
elution holes provided between the adjacent reinforcing core
materials was 2 and the distance c.sub.2 between the adjacent
elution holes was 432 .mu.m. According to calculation, distance
c.sub.2 was expressed by 1.17a.sub.2/(n+1) (see FIG. 8, the same
hereinafter).
[0156] Furthermore, in the TD direction, in the distance a.sub.1
between the reinforcing core materials adjacent to each other of
1056 .mu.m, the number n of elution holes provided between the
adjacent reinforcing core materials was 2 and the distance c.sub.1
of the adjacent elution holes was 203 .mu.m. According to
calculation, the distance c.sub.1 was expressed by
0.58a.sub.1/(n+1).
[0157] Moreover, in the MD direction, in the distance a.sub.2
between the reinforcing core materials adjacent to each other of
1192 .mu.m, the number n of elution holes provided between the
adjacent reinforcing core materials was 2 and the distance c.sub.2
of the adjacent elution holes was 528 .mu.m. According to
calculation, the distance c.sub.2 was expressed by
1.33a.sub.2/(n+1).
[0158] In the MD direction, in the distance a.sub.1 between the
reinforcing core materials adjacent to each other of 998 .mu.m, the
number n of elution holes provided between the adjacent reinforcing
core materials was 2 and the distance c.sub.1 of the adjacent
elution holes was 296 .mu.m. According to calculation, the distance
c.sub.1 was expressed by 0.89a.sub.1/(n+1).
[0159] The physical properties of the obtained cation exchange
membrane are shown in Table 1. In Table 1, the interval units
between reinforcing core materials, which were alternately arranged
in adjacent to each other in the TD direction of the cation
exchange membrane in Example 1 were respectively designated as
reinforcing core material interval T1 and reinforcing core material
interval T2. Furthermore, In the MD direction, repeated
constitutional units were designated as reinforcing core material
interval M1 and reinforcing core material interval M2. Also as to
the following Examples and Comparative Examples, description was
made in the table similarly. As shown in Table 1, it was confirmed
that the cation exchange membrane had a high tensile elongation
retaining rate in either one of MD folding and TD folding.
Example 2
[0160] A cation exchange membrane was prepared by using the same
materials as in Example 1 except that a yarn (PVA yarn) of
15-filament polyvinyl alcohol (PVA) of 28 deniers twisted 200
times/m was used as a dummy yarn.
[0161] In the obtained cation exchange membrane, in the TD
direction, the distance a.sub.2 between the reinforcing core
materials adjacent to each other was 1005 .mu.m, the number n of
elution holes provided between the adjacent reinforcing core
materials was 2 and the distance c.sub.2 of the adjacent elution
holes was 373 .mu.m. According to calculation, the distance c.sub.2
was expressed by 1.11a.sub.2/(n+1) (see FIG. 8, the same
hereinafter).
[0162] Furthermore, in the TD direction, in the distance a.sub.1
between the reinforcing core materials adjacent to each other of
1091 .mu.m, the number n of elution holes provided between the
adjacent reinforcing core materials was 2 and the distance c.sub.1
of the adjacent elution holes was 252 .mu.m. According to
calculation, the distance c.sub.1 was expressed by
0.69a.sub.1/(n+1).
[0163] Moreover, in the MD direction, in the distance a.sub.2
between the reinforcing core materials adjacent to each other of
1199 .mu.m, the number n of elution holes provided between the
adjacent reinforcing core materials was 2 and the distance c.sub.2
of the adjacent elution holes was 500 .mu.m. According to
calculation, the distance c.sub.2 was expressed by
1.25a.sub.2/(n+1).
[0164] In the MD direction, in the distance a.sub.1 between the
reinforcing core materials adjacent to each other of 999 .mu.m, the
number n of elution holes provided between the adjacent reinforcing
core materials was 2 and the distance c.sub.1 between the adjacent
elution holes was 266 .mu.m. According to calculation, the distance
c.sub.1 was expressed by 0.80a.sub.1/(n+1).
[0165] The physical properties of the obtained cation exchange
membrane are shown in Table 1. As shown in Table 1, it was
confirmed that the cation exchange membrane had a high tensile
elongation retaining rate in either one of MD folding and TD
folding.
Example 3
[0166] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 3-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PTFE yarn was passed through
a second reed; and a bundle of 2 yarns consisting of PET yarn and
PET yarn was passed through a third reed. Weaving of the bundles of
yarns in this combination was repeated in this order to obtain a
plain weave. As to TD yarns, PTFE yarn, PVA yarn, PVA yarn, PET
yarn, PET yarn, PVA yarn and PVA yarn were arranged in this order
repeatedly and at approximately equal intervals to obtain a plain
weave. In this manner, a woven fabric (reinforcing material) was
obtained. Subsequently, the obtained reinforcing material was
subjected to contact bonding performed by a roll heated to
125.degree. C. Thereafter, the reinforcing material was soaked in a
0.1 N aqueous sodium hydroxide solution to dissolve a dummy yarn
(PVA yarn) alone and remove it from the reinforcing material. The
thickness of the reinforcing material from which the dummy yarn was
removed was 85 .mu.m. A cation exchange membrane was prepared in
the same manner as in Example 1 except the above.
[0167] In the obtained cation exchange membrane, in the TD
direction, the distance a.sub.1 between the reinforcing core
materials adjacent to each other was 1119 .mu.m, the number n of
elution holes provided between the adjacent reinforcing core
materials was 2 and the distance c.sub.1 of the adjacent elution
holes was 255 .mu.m. According to calculation, the distance c.sub.1
was expressed by 0.68a.sub.1/(n+1) (see FIG. 8, the same
hereinafter).
[0168] Furthermore, in the MD direction, the distance a.sub.2
between the reinforcing core materials adjacent to each other was
1229 .mu.m, the number n of elution holes provided between the
adjacent reinforcing core materials was 2 and the distance c.sub.2
of the adjacent elution holes was 569 .mu.m. According to
calculation, the distance c.sub.2 was expressed by
1.39a.sub.2/(n+1).
[0169] Moreover, in the MD direction, the distance a.sub.1 between
the reinforcing core materials adjacent to each other was 985
.mu.m, the number n of elution holes provided between the adjacent
reinforcing core materials was 2 and the distance c.sub.1 of the
adjacent elution holes was 323 .mu.m. According to calculation, the
distance c.sub.1 was expressed by 0.98a.sub.1/(n+1).
[0170] The physical properties of the obtained cation exchange
membrane are shown in Table 1. As shown in Table 1, it was
confirmed that the cation exchange membrane had a high tensile
elongation retaining rate in either one of MD folding and TD
folding.
Example 4
[0171] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 3-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PTFE yarn was passed through
a second reed and a bundle of 2 yarns consisting of PET yarn and
PET yarn was passed through a third reed. Weaving of the bundles of
yarns in this combination was repeated in this order to obtain a
plain weave. As to TD yarns, PTFE yarn, PET yarn and PET yarn were
arranged at approximately equal interval sequentially in this order
repeatedly to obtain a plain weave. In this manner, a woven fabric
(reinforcing material) was obtained. Subsequently, the obtained
reinforcing material was subjected to contact bonding performed by
a roll heated to 125.degree. C. Thereafter, the obtained
reinforcing material was soaked in a 0.1 N aqueous sodium hydroxide
solution to dissolve a dummy yarn (PVA yarn) alone and remove it
from the reinforcing material. The thickness of the reinforcing
material from which the dummy yarn was removed was 76 .mu.m. A
cation exchange membrane was prepared in the same manner as in
Example 1 except the above.
[0172] In the obtained cation exchange membrane, in the TD
direction, the distance a.sub.1 between the reinforcing core
materials adjacent to each other was 1092 .mu.m, the number n of
elution holes provided between the adjacent reinforcing core
materials was 2 and the distance c.sub.1 between the adjacent
elution holes was 364 .mu.m. According to calculation, the distance
c.sub.1 was expressed by 1.00a.sub.1/(n+1).
[0173] In the MD direction, the distance a.sub.2 between the
reinforcing core materials adjacent to each other was 1178 .mu.m,
the number n of elution holes provided between the adjacent
reinforcing core materials was 2 and the distance c.sub.2 of the
adjacent elution holes was 509 .mu.m. According to calculation, the
distance c.sub.2 was expressed by 1.30a.sub.2/(n+1) (see FIG. 8,
the same hereinafter).
[0174] In the MD direction, the distance a.sub.1 between the
reinforcing core materials adjacent to each other was 930 .mu.m,
the number n of elution holes provided between the adjacent
reinforcing core materials was 2 and the distance c.sub.1 between
the adjacent elution holes was 253 .mu.m. According to calculation,
the distance c.sub.1 was expressed by 0.82a.sub.1/(n+1).
[0175] The physical properties of the obtained cation exchange
membrane are shown in Table 1. As shown in Table 1, it was
confirmed that the cation exchange membrane had a high tensile
elongation retaining rate in TD folding.
Comparative Example 1
[0176] A cation exchange membrane was produced having elution holes
formed at equal intervals both in the MD direction and in the TD
direction. As a reinforcing core material, a monofilament made by
polytetrafluoroethylene (PTFE) of 90 deniers (PTFE yarn) was used.
As a sacrifice yarn, a yarn formed of 6-filament polyethylene
terephthalate (PET) of 40 deniers and twisted at a rate of 200
twists/m (PET yarn) was used.
[0177] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at equal intervals. As to MD yarns, PTFE yarn, PET yarn and PET
yarn . . . were arranged in this order repeatedly to obtain a plain
weave. Also as to TD yarns, PTFE yarn, PET yarn and PET yarn . . .
were arranged repeatedly to obtain a plain weave. In this manner, a
woven fabric (reinforcing material) was obtained. Subsequently, the
obtained reinforcing material was subjected to contact bonding
performed by a roll heated and controlled so as to have a thickness
of 86 .mu.m. The cation exchange membrane was obtained in the same
manner as in Example 1 except the above.
[0178] In the cation exchange membrane, in the TD direction, the
distance a.sub.1 between the reinforcing core materials adjacent to
each other was 1058 .mu.m, the number n of elution holes provided
between the adjacent reinforcing core materials was 2 and the
distance c.sub.1 of the adjacent elution holes was 353 .mu.m.
According to calculation, the distance c.sub.1 was expressed by
1.00a.sub.1/(n+1) (see FIG. 8, the same hereinafter).
[0179] In the MD direction, the distance a.sub.1 between the
reinforcing core materials adjacent to each other was 1058 .mu.m,
the number n of elution holes provided between the adjacent
reinforcing core materials was 2 and the distance c.sub.1 between
the adjacent elution holes was 353 .mu.m. According to calculation,
the distance c.sub.1 was expressed by 1.00a.sub.1/(n+1).
[0180] The physical properties of the cation exchange membranes of
Examples 1 to 4 and Comparative Example 1 are shown in Table 1.
Note that, the symbol "-" in the table indicates that no
corresponding substance is present in Examples and Comparative
Examples. As shown in Table 1, it was confirmed that the cation
exchange membrane of each Example had a high tensile elongation
retaining rate in either one of MD folding and TD folding.
TABLE-US-00001 TABLE 1 Comparative Example 1 Example 2 Example 3
Example 4 Example 1 Reinforcing Material PTFE PTFE PTFE PTFE PTFE
yarn Denier 90 90 90 90 90 Filament mono mono mono mono mono
Sacrifice Material PET PET PET PET PET yarn Denier 30 30 40 40 40
Filament 6 6 6 6 6 Twisting 200 200 200 200 200 times Dummy
Material PVA PVA PVA -- -- yarn Denier 36 28 36 -- -- Filament 15
15 15 -- -- Twisting 200 200 200 -- -- times Thickness of
reinforcing material 81 84 85 76 86 (.mu.m) n 2 2 2 2 2 Yarn T1
a.sub.1 1056 1091 1119 1092 1058 interval b.sub.1 426.5 419.5 432
364 352.5 (TD direction) c.sub.1 203 252 255 364 353
b.sub.1/(a.sub.1/ 1.21 1.15 1.16 1.00 1.00 (n + 1))
c.sub.1/(a.sub.1/ 0.58 0.69 0.68 1.00 1.00 (n + 1)) T2 a.sub.2 1112
1005 -- -- -- b.sub.2 340 316 -- -- -- c.sub.2 432 373 -- -- --
c.sub.2/(a.sub.2/ 1.17 1.11 -- -- -- (n + 1)) Yarn M1 a.sub.1 998
999 985 930 1058 interval b.sub.1 351 366.5 331 338.5 352.5 (MD
direction) c.sub.1 296 266 323 253 353 b.sub.1/(a.sub.1/ 1.06 1.10
1.01 1.09 1.00 (n + 1)) c.sub.1/(a.sub.1/ 0.89 0.80 0.98 0.82 1.00
(n + 1)) M2 a.sub.2 1192 1199 1229 1178 -- b.sub.2 332 349.5 330
334.5 -- c.sub.2 528 500 569 509 -- c.sub.2/(a.sub.2/ 1.33 1.25
1.39 1.30 -- (n + 1)) Folding resistance MD 63 51 58 42 41 (%)
(Tensile Folding elongation TD 72 76 70 82 41 retention rate (%))
Folding
Example 5
[0181] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 3-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PTFE yarn was passed through
a second reed; and a bundle of 2 yarns consisting of PET yarn and
PET yarn was passed through a third reed. Weaving of the bundles of
yarns in this combination was repeated in this order to obtain a
plain weave. As to TD yarns, PTFE yarn, PET yarn, PVA yarn, PVA
yarn, PVA yarn, PVA yarn and PET yarn were arranged in this order
repeatedly and at approximately equal intervals to obtain a plain
weave. In this manner, a woven fabric (reinforcing material) was
obtained. Subsequently, the obtained reinforcing material was
subjected to contact bonding performed by a roll heated to
125.degree. C. Thereafter, the reinforcing material was soaked in a
0.1 N aqueous sodium hydroxide solution to dissolve a dummy yarn
(PVA yarn) alone and remove it from the reinforcing material. The
thickness of the reinforcing material from which the dummy yarn was
removed was 85 .mu.m. A cation exchange membrane was prepared in
the same manner as in Example 1 except the above.
[0182] In the cation exchange membrane, in the TD direction, the
distance a.sub.1 between the reinforcing core materials adjacent to
each other was 1040 .mu.m, the number n of elution holes provided
between the adjacent reinforcing core materials was 2 and the
distance c.sub.1 between the adjacent elution holes was 448 .mu.m.
Accordingly, the distance c.sub.1 was expressed by
1.29a.sub.1/(n+1) (see FIG. 8, the same hereinafter). In the TD
direction of the cation exchange membrane of Example 5, the only
the interval between reinforcing core materials having the
aforementioned a1, b1, c1 values was arranged.
[0183] In the MD direction, the distance a.sub.2 between the
reinforcing core materials adjacent to each other was 1151 .mu.m,
the number n of elution holes provided between the adjacent
reinforcing core materials was 2 and the distance c.sub.2 between
the adjacent elution holes was 478 .mu.m. Accordingly, the distance
c.sub.2 was expressed by 1.25a.sub.2/(n+1). In the MD direction,
the distance a.sub.1 between the reinforcing core materials
adjacent to each other was 944 .mu.m, the number n of elution holes
provided between the adjacent reinforcing core materials was 2 and
the distance c.sub.1 of the adjacent elution holes was 269 .mu.m.
Accordingly, the distance c.sub.1 was expressed by
0.85a.sub.1/(n+1).
[0184] As evaluation of mechanical strength, the cation exchange
membrane was folded by applying weight of 400 g/cm.sup.2 so as to
allow the surface of the carboxylic acid layer side (see FIG. 1,
the carboxylic acid layer 144, and "polymer A layer" described
above) to face inside and the presence or absence of e.g., pinhole
formation was observed. In the obtained cation exchange membrane of
Example 5, formation of a pinhole by folding was not confirmed.
[0185] In Examples 1 to 5 and Comparative Example 1, electrolysis
was performed by use of the obtained cation exchange membrane and
electrolysis voltage was measured. The results are shown in Table
2.
TABLE-US-00002 TABLE 2 Compar- Exam- Exam- Exam- Exam- Exam- ative
ple 1 ple 2 ple 3 ple 4 ple 5 Example 1 Electrolysis 3.22 3.26 3.31
3.37 3.30 3.45 voltage (V)
[0186] As shown in Table 2, when electrolysis was performed by
using the cation exchange membrane of each Example, it was
confirmed that electrolysis voltage was reduced compared to
Comparative Example 1. Furthermore, when an electrolysis operation
was performed for 7 days, electrolysis could be stably
performed.
[0187] From the above, it was demonstrated that the cation exchange
membrane of each Example was excellent in mechanical strength
against folding, etc. As a result, it was demonstrated that stable
electrolytic performance can be delivered for a long time. It was
further demonstrated that, in the cation exchange membrane of each
Example, electrolysis voltage can be reduced compared to the cation
exchange membrane where elution holes were formed at equal
intervals, and excellent electrolytic performance can be
delivered.
Example 6
[0188] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 5-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PET yarn was passed through a
second reed; a bundle of 2 yarns consisting of PET yarn and PTFE
yarn was passed through a third reed; a bundle of 2 yarns
consisting of PET yarn and PET yarn was passed through a fourth
reed; and a bundle of 2 yarns consisting of PET yarn and PET yarn
was passed through a fifth reed. Weaving of the bundles of yarns in
this combination was repeated in this order to obtain a plain
weave. As to TD yarns, PTFE yarn, PET yarn, PET yarn, PVA yarn, PVA
yarn, PET yarn and PET yarn were arranged in this order repeatedly
and at approximately equal intervals to obtain a plain weave. In
this manner, a woven fabric (reinforcing material) was obtained.
Subsequently, the obtained reinforcing material was subjected to
contact bonding performed by a roll heated to 125.degree. C.
Thereafter, the obtained reinforcing material was soaked in a 0.1 N
aqueous sodium hydroxide solution to dissolve a dummy yarn (PVA
yarn) alone and remove it from the reinforcing material. The
thickness of the reinforcing material from which the dummy yarn was
removed was 93 .mu.m. The cation exchange membrane 8 shown in FIG.
9 was prepared in the same manner as in Example 1 except the above.
The cation exchange membrane 8 had the membrane body (not shown)
and two or more reinforcing core materials 80 arranged
approximately in parallel within the membrane body. The membrane
body had a structure where 4 elution holes were formed between the
reinforcing core materials 80 adjacent to each other. More
specifically, four elution holes 821, 822, 823, 824 were formed at
respective intervals of a, b, c.sub.1, c.sub.2 between the
reinforcing core materials 80.
[0189] In the obtained cation exchange membrane, in the TD
direction, the distance a between the reinforcing core materials
adjacent to each other was 1521 .mu.m, the number n of elution
holes provided between the adjacent reinforcing core materials was
4, the distance b of the reinforcing core material and the adjacent
elution hole was 268 .mu.m and the distance c.sub.1 between the
elution hole and the adjacent elution hole was 265 .mu.m. The
distance c.sub.2 between the two elution holes at the center was
443 .mu.m (see FIG. 9).
[0190] Furthermore, in the MD direction, elution holes were formed
at equal intervals between the reinforcing core materials.
[0191] The physical properties of the obtained cation exchange
membrane are shown in Table 3. As is shown in Table 3, it was
confirmed that the cation exchange membrane had a high tensile
elongation retaining rate in MD folding compared to Comparative
Example 2. Furthermore, it was confirmed that the electrolysis
voltage thereof was lower than that of Comparative Example 2.
Example 7
[0192] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 5-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PET yarn was passed through a
second reed; a bundle of 2 yarns consisting of PET yarn and PTFE
yarn was passed through a third reed; a bundle of 2 yarns
consisting of PET yarn and PET yarn was passed through a fourth
reed; and a bundle of 2 yarns consisting of PET yarn and PET yarn
was passed through a fifth reed. Weaving of the bundles of yarns in
this combination was repeated in this order to obtain a plain
weave. As to TD yarns, PTFE yarn, PET yarn, PVA yarn, PVA yarn, PET
yarn, PET yarn, PVA yarn, PVA yarn and PET yarn were arranged in
this order repeatedly and at approximately equal intervals to
obtain a plain weave. In this manner, a woven fabric (reinforcing
material) was obtained. Subsequently, the obtained reinforcing
material was subjected to contact bonding performed by a roll
heated to 125.degree. C. Thereafter, the reinforcing material was
soaked in a 0.1 N aqueous sodium hydroxide solution to dissolve a
dummy yarn alone and remove it from the reinforcing material. The
thickness of the reinforcing material from which the dummy yarn was
removed was 93 .mu.m. A cation exchange membrane was prepared in
the same manner as in Example 6 except the above.
[0193] In the cation exchange membrane, in the TD direction, the
distance a between the reinforcing core materials adjacent to each
other was 1523 .mu.m, the number n of elution holes provided
between the adjacent reinforcing core materials was 4, the distance
b of the reinforcing core material and the adjacent elution hole
was 264 .mu.m and the distance c.sub.1 of the elution hole and the
adjacent elution hole was 361 .mu.m. The distance c.sub.2 between
the two elution holes at the center was 245 .mu.m (see FIG. 9).
[0194] Furthermore, in the MD direction, elution holes were formed
at equal intervals between the reinforcing core materials.
Comparative Example 2
[0195] A cation exchange membrane was produced having elution holes
formed at equal intervals both in the MD direction and in the TD
direction. As a reinforcing core material, a monofilament
polytetrafluoroethylene (PTFE) of 90 deniers (PTFE yarn) was used.
As a sacrifice yarn, 6-filament polyethylene terephthalate (PET) of
40 deniers twisted at a rate of 200 twists/m (PET yarn) was
used.
[0196] First, PTFE yarns were arranged at a rate of 16 yarns/inch
at equal intervals. As to MD yarn, PTFE yarn, PET yarn, PET yarn,
PET yarn and PET yarn were arranged in this order repeatedly to
obtain a plain weave. Also as to TD yarn, PTFE yarn, PET yarn, PET
yarn, PET yarn and PET yarn were arranged repeatedly to obtain a
plain weave thereby producing a woven fabric (reinforcing
material). Subsequently, the obtained reinforcing material was
subjected to contact bonding performed by a roll heated to
125.degree. C. and controlled so as to have a thickness of 85
.mu.m. A cation exchange membrane was obtained in the same manner
as in Example 6 except the above.
[0197] In the cation exchange membrane, in the TD direction, the
distance a between the reinforcing core materials adjacent to each
other was 1517 .mu.m, the number n of elution holes provided
between the adjacent reinforcing core materials was 4, the distance
b between the reinforcing core material and the adjacent elution
hole was 303 .mu.m and the distance c.sub.1 between the elution
hole and the adjacent elution hole was 303 .mu.m. The distance
c.sub.2 between the two elution holes at the center was 303 .mu.m
(see FIG. 9).
[0198] Furthermore, in the MD direction, elution holes were formed
at equal intervals between the reinforcing core materials.
[0199] The physical properties of the cation exchange membranes of
Example 6, 7 and Comparative Example 2 are shown in Table 3. As
shown in Table 3, in Example 6, 7, it was confirmed that the cation
exchange membrane had a high tensile elongation retaining rate also
after folding. Furthermore, as is shown in Table 3, when
electrolysis was performed by using the cation exchange membrane of
each Example, it was confirmed that electrolysis voltage was
reduced compared to Comparative Example 2. Furthermore, when an
electrolysis operation was performed for 7 days, electrolysis can
be stably performed.
TABLE-US-00003 TABLE 3 Comparative Example 6 Example 7 Example 2
Reinforcing Material PTFE PTFE PTFE yarn Denier 90 90 90 Filament
mono mono mono Sacrifice yarn Material PET PET PET Denier 30 40 40
Filament 6 6 6 Twisting times 200 200 200 Dummy yarn Material PVA
PVA PVA Denier 36 36 36 Filament 15 15 15 Twisting times 200 200
200 Thickness of reinforcing material 93 93 85 (.mu.m) n 4 4 4 Yarn
TD direction a 1521 1523 1517 interval b 268 264 303 c.sub.1 265
361 303 c.sub.2 443 245 303 c.sub.1/(a/(n + 0.9 1.2 1.0 1))
c.sub.2/(a/(n + 1.5 0.8 1.0 1)) Folding resistance (%) MD 44 44 28
(Tensile elongation Folding retention rate (%)) Electrolysis
voltage (V) 3.26 3.26 3.31
[0200] From the above, it was demonstrated that the cation exchange
membrane of each Example was excellent in mechanical strength
against folding, etc. As a result, it was demonstrated that
electrolytic performance could be stably delivered for a long time.
Furthermore, it was demonstrated that in the case where the cation
exchange membrane of each Example was used, electrolysis voltage
could be reduced compared to the case where the cation exchange
membrane having the reinforcing core materials where elution holes
were formed at equal intervals, and that excellent electrolytic
performance could be delivered.
Example 8
[0201] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 5-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PET yarn was passed through a
second reed; a bundle of 2 yarns consisting of PET yarn and PTFE
yarn was passed through a third reed; a bundle of 2 yarns
consisting of PET yarn and PET yarn was passed through a fourth
reed; and a bundle of 2 yarns consisting of PET yarn and PET yarn
was passed through a fifth reed. Weaving of the bundles of yarns in
this combination was repeated in this order to obtain a plain
weave. As to TD yarns, PTFE yarn, PVA yarn, PVA yarn, PET yarn, PET
yarn, PET yarn, PET yarn, PVA yarn and PVA yarn were arranged in
this order repeatedly and at approximately equal intervals to
obtain a plain weave. In this manner, a woven fabric (reinforcing
material) was obtained. Subsequently, the obtained reinforcing
material was subjected to contact bonding performed by a roll
heated to 125.degree. C. Thereafter, the reinforcing material was
soaked in a 0.1 N aqueous sodium hydroxide solution to dissolve a
dummy yarn (PVA yarn) alone and remove it from the reinforcing
material. The thickness of the reinforcing material from which the
dummy yarn was removed was 95 .mu.m. A cation exchange membrane was
prepared in the same manner as in Example 1 except the above.
[0202] In the obtained cation exchange membrane, in the TD
direction, the distance a between the reinforcing core materials
adjacent to each other was 1559 .mu.m, the number n of elution
holes provided between the adjacent reinforcing core materials was
4, the distance b of the reinforcing core material and the adjacent
elution hole was 463 .mu.m and the distance c.sub.1 of the elution
hole and the adjacent elution hole was 206 .mu.m. The distance
c.sub.2 between the two elution holes at the center was 180 .mu.m
(see FIG. 9).
Example 9
[0203] First, PTFE yarns were arranged at a rate of 24 yarns/inch
at approximately equal intervals. MD yarns were prepared by use of
a continuous 5-dent reed as follows. A bundle of 2 yarns consisting
of PTFE yarn and PET yarn was passed through a first reed; a bundle
of 2 yarns consisting of PET yarn and PET yarn was passed through a
second reed; a bundle of 2 yarns consisting of PET yarn and PTFE
yarn was passed through a third reed; a bundle of 2 yarns
consisting of PET yarn and PET yarn was passed through a fourth
reed; and a bundle of 2 yarns consisting of PET yarn and PET yarn
was passed through a fifth reed. Weaving of the bundles of yarns in
this combination was repeated in this order to obtain a plain
weave. As to TD yarns, PTFE yarn, PET yarn, PET yarn, PVA yarn, PVA
yarn, PET yarn, PET yarn, PTFE yarn, PET yarn, PVA yarn, PVA yarn,
PET yarn, PET yarn, PVA yarn, PVA yarn and PET yarn were arranged
in this order repeatedly and at approximately equal intervals to
obtain a plain weave. In this manner, a woven fabric (reinforcing
material) was obtained. Subsequently, the obtained reinforcing
material was subjected to contact bonding performed by a roll
heated to 125.degree. C. Thereafter, the reinforcing material was
soaked in a 0.1 N aqueous sodium hydroxide solution to dissolve a
dummy yarn (PVA yarn) alone and remove it from the reinforcing
material. The thickness of the reinforcing material from which the
dummy yarn was removed was 92 .mu.m. The cation exchange membrane
was prepared in the same manner as in Example 1 except the
above.
[0204] In the obtained cation exchange membrane, in the TD
direction, the distance a between the reinforcing core materials
adjacent to each other was 1743 .mu.m, the number n of elution
holes provided between the adjacent reinforcing core materials was
4, the distance b between the reinforcing core material and the
adjacent elution hole was 201 .mu.m and the distance c.sub.1
between the elution hole and the adjacent elution hole was 470
.mu.m. The distance c.sub.2 between the two elution holes at the
center was 255 .mu.m (see FIG. 9).
[0205] Furthermore, in the case where the distance a between the
reinforcing core materials adjacent to each other was 1387 .mu.m,
the number n of elution holes provided between the adjacent
reinforcing core materials was 4 and the distance b between the
reinforcing core material and the adjacent elution hole was 228
.mu.m and the distance c.sub.1 between the elution hole and the
adjacent elution hole was 462 .mu.m. The distance c.sub.2 between
the two elution holes at the center was 218 .mu.m (see FIG. 9).
[0206] The physical properties of the cation exchange membranes of
Examples 8 and 9 are shown in Table 4. Note that, the symbol "-" in
the table indicates that no corresponding substance was present in
the Examples and Comparative Examples.
TABLE-US-00004 TABLE 4 Example 8 Example 9 Reinforcing yarn
Material PTFE PTFE Denier 90 90 Filament mono mono Sacrifice yarn
Material PET PET Denier 40 40 Filament 6 6 Twisting times 200 200
Dummy yarn Material PVA PVA Denier 36 36 Filament 15 15 Twisting
times 200 200 Thickness of reinforcing material (.mu.m) 95 92 N 4 4
Yarn interval (TD direction) T1 A 1559 1743 B 463 201 c.sub.1 206
470 c.sub.2 180 255 c.sub.1/(a/(n + 1)) 0.66 1.35 c.sub.2/(a/(n +
1)) 0.58 0.73 T2 A -- 1387 B -- 228 c.sub.1 -- 462 c.sub.2 -- 218
c.sub.1/(a/(n + 1)) -- 1.67 c.sub.2/(a/(n + 1)) -- 0.79
[0207] As evaluation of mechanical strength, the cation exchange
membrane was folded by applying weight of 400 g/cm.sup.2 so as to
allow the surface of the carboxylic acid layer side (see FIG. 1,
the carboxylic acid layer 144, and "polymer A layer" described
above) to face inside and the presence or absence of e.g., pinhole
formation was observed. In the obtained cation exchange membrane of
Examples 8 and 9, formation of a pinhole by folding was not
confirmed. In addition, it was discovered that stable electrolytic
performance can be delivered for a long time.
[0208] This application is based on Japanese Patent Application No.
2009-245869 which was filed with Japan Patent Office on Oct. 26,
2009, which is hereby incorporated by reference herein.
INDUSTRIAL APPLICABILITY
[0209] The cation exchange membrane of the present invention can be
suitably used as the cation exchange membrane for alkali chloride
electrolysis, etc.
REFERENCE SIGNS LIST
[0210] 1, 2, 3, 4, 5 . . . Cation exchange membrane, [0211] 6 . . .
Reinforcing material, [0212] 10, 20x, 20y, 301, 302, 303, 401, 402,
403, 501x, 501y, 502x, 502y, 503x, 503y, 60 . . . Reinforcing core
material, [0213] 12, 12a, 12b, 22x, 22y, 321, 322, 323, 324, 325,
326, 421, 422, 423, 424, 521x, 521y, 522x, 522y, 523x, 523y, 524x,
524y . . . Elution holes, [0214] 14 . . . Membrane body, [0215] 62
. . . Sacrifice yarn, [0216] 66 . . . Dummy yarn, [0217] 142 . . .
Sulfonic acid layer, [0218] 144 . . . Carboxylic acid layer, [0219]
146, 148 . . . Coating layer, [0220] A . . . Electrolysis vessel,
[0221] A1 . . . Anode, [0222] A2 . . . Cathode, [0223] .alpha. . .
. Anode side, [0224] .beta. . . . Cathode side, [0225] X . . . MD
direction, [0226] Y . . . TD direction
* * * * *